This writeup suggests substitutes:I've quoted the most promising option.
It seems that Vietnamese Coriander is not really from the coriander family and closely mimics the flavor of cilantro.
Let me know if this works.
Vietnamese coriander or Persicaria odorata is a herb, the leaves of which commonly feature in Southeast Asian cuisine, particularly in Vietnam and Malaysia.
It is also known by the name of Vietnamese cilantro, Vietnamese mint and Cambodian mint.
Though it is not related to mint, its flavor as well as appearance can be said to slightly resemble mint.
It is more commonly included in salads and soups.
The flavor of Vietnamese coriander closely mimics the flavor of cilantro, and hence, can be used as a cilantro substitute.
This herb is believed to be very effective for some common gastrointestinal problems like, indigestion, stomachache and flatulence.
cooking.stackexchange.com/users/2125/milesmeow
I would try Lime Basil or a mixture of 1/2 vinegar, and 1/2 bottled lime juice (small portion).
cooking.stackexchange.com/users/177/AttilaNYC
I am one of the people that love the taste of Cilantro (and Coriander) - Cilantro tastes like as if it should be called lemon Parsley to me - so my suggestion would be to replace it half and half with Parsely/Lemon Balm or Pasley
/Lemon Thyme depending on the region the dish is from.
If it is a SE Asian dish, you might also be able to substitute Lemon Grass and Parsley.
I would only use Flat leaf Parsley as it isn't as bitter and tastes more "green" than curly leaf Parsley.
Lemon Balm and Lemon Grass on their own taste too much of Lemon, Parlsey on it's own is too dull.
cooking.stackexchange.com/users/37673/Sabine
If you are cooking a curry or Asian dish, perhaps Thai basil or purple basil would work instead.
If you are cooking a Mexican style dish, Mexican oregano might also be a good choice.
I have also read that celery leaves are a good substitute, but they can be tricky to find as most stores only sell the stalks.
Sometimes you can find bunches at the Farmer's Market that still have the leaves attached.
I would also suggest carrot greens, which will have a similar appearance but still impart some flavor.
These might pack more of a flavor punch than just parsley.
cooking.stackexchange.com/users/1769/Jenn
I too have the so-called "soap-gene", but after 8 years living in Mexico, I have come to tolerate cilantro.
Still, for several years I sought alternatives.
Parsley is not, except visually.
A mix of parsley, lemon basil or lime basil, and beet or radish or celery leaves isn't too far off, and lacks the soap thang.
A very small bit of yerba buena, mixed with Mexican oregano, and maybe a bit of basil, gets a similar point across, but don't use too much, because it is a member of the salvia fairly closely related to spearmint -- great on a cucumber and onion salad or cucumber yogurt dressing on salmon, but not quite right on tacos.
Someone above said fresh coriander, but that is silly -- fresh coriander is cilantro.
And ground coriander seeds are used extensively in Mexican cooking, but do not replace cilantro.
cooking.stackexchange.com/users/68385/Albert Cornelius Doyle
Papalo - cilantro on steroids.
cooking.stackexchange.com/users/50705/Chef Hollobaugh
For the special case of just using it as a green, herby garnish on top of an asian dish: In some cases, thinly sliced spring onion greens will do fine (different flavor, same function: be green and provide a visual and flavour-wise contrast to the cooked ingredients).
cooking.stackexchange.com/users/35312/rackandboneman
Culantro (eryngium foetidum) seems to have many of the flavors of cilantro without the soap taste.
I can't say for certainty how similar they are, because the soap flavor is so overwhelming to me.
The wikipedia page says that culantro is stronger.
(but I can put lots into a dish, and not gag)
I have no idea if it would still trigger your dad's allergies, though.
They're both in the Apiaceae family.
The only place that I can find it in Maryland is in latin markets, or the larger international markets (that cater towards asian & latin communities).
It's a long, narrow leaf (sort of a stretched oval.
See wikipedia , although the cultivated stuff is closer to 12" (30cm)).
It's often in plastic bags in the store (as it can dry out fairly quickly, but it holds okay in your fridge for a week or two if you wrap it in paper towels and then re-bag it)
cooking.stackexchange.com/users/67/Joe
Out of 3 different recipe books, I see they swap parsley for cilantro.
Not sure if you will get the flavor that you are looking for there, though.
cooking.stackexchange.com/users/586/mbowles
I'm doing 1/3 each mix of basil, parsley, and lemon peel in my tandoori based dish.
I forgot the cilantro and dont have thai basil or those other "exotic" spices laying around.
Wish me luck.
cooking.stackexchange.com/users/53589/Covertsphinx
Also have the soap-taste problem.
I agree that parsley is more a substitute in looks rather than flavor.
I tend to use either arugula or watercress as they have a bit of a bite that at least let's you know they're there.
I like the idea of celery leaves.
Maybe will try mincing a three of them up together!
cooking.stackexchange.com/users/73066/m La Touche
I have several friends with the soap gene (cilantro tastes like soap to them), my father's allergic (it gives him a headache) and because of a lifetime of avoiding the stuff, I find cilantro overwhelming in just about everything.   Typically, I substitute parsley, but sometimes it still feels like the dish is missing something. Are there other good substitutes for cilantro, either individual herbs or combinations?
What's a good substitute for cilantro?
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<substitutions><cilantro>
cooking.stackexchange.com/questions/7078
cooking.stackexchange.com/users/2251/In the Booley House
Vietnamese coriander is not related, but closely mimics the flavour of cilantro. Different basils, parsley, beet, radish or celery leaves, lemon balm, carrot greens, papalo, culantro, arugula and watercress can approximate the taste, and vinegar and lemon juice or peel may also help. There are a lot of different herbs that comes close to cilantro. There are several varieties of basil, celery and carrot leaves, then other herbs like culantro or papalo.
A mix of parsley, lemon basil or lime basil, and beet or radish or celery leaves isn't too far off, and lacks the soap thang.
Try Vietnamese coriander. Try Thai, lime or purple basil. Try parsely and lemon balm, celery leaves, carrot greens, papalo, culantro or watercress.