The main things that Parmesan cheese can add to a salad are fattiness and salt.
The first thing that comes to mind for me is bacon.
You could probably also make a yummy main dish salad (or hearty first course) by adding duck or a cured meat such as salami.
If you're not interested in adding meat, how about olives?
Those would serve similar purposes.
Other options might be marinated artichoke hearts or mushrooms.
Just make sure you choose ones that aren't too tart, as they might add to the effect of the lemon vinaigrette.
cooking.stackexchange.com/users/1887/Martha F.
I agree with Martha with the fat a salt being the required balancing element in a bitter salad but think with your delicate flavours bacon might over power.
I think I'd add an air died ham like Serrano or Parma ham.
cooking.stackexchange.com/users/2391/vwiggins
My sister's dairy-free out of necessity (milk allergy, not lactose intolerance) and she swears by a mixture of baker's yeast, breadcrumbs, garlic powder, and salt for Parmesan replacement, though obviously it's more akin to grated cheese than sliced cheese and thus might not be the texture you want.
cooking.stackexchange.com/users/2251/In the Booley House
On endive salad, I like to cut bitterness with sumak , a spice commonly used in Turkey as a replacement for lemon juice.
cooking.stackexchange.com/users/2402/mouviciel
As someone who is also dairy and gluten free, first off you can make gluten-free bread crumbs now, with some decent gluten free breads on the market (I've also found gf crumbs in high-end grocery stores).
Second, I will often cut the bitterness with a high-quality olive oil (California Olive Ranch is sweeter), with a nice large-grain salt, and/or with balsamic vinegar which can add sweetness as well.
Depending on the dish, mirin can also add sweetness.
If you substitute with olives, try Graber olives or Castelveltrano (my favorite!).
Or try avocado or a ripe heirloom tomato.
Or both.
Have fun and good luck!
cooking.stackexchange.com/users/40389/jthomason
Try shredded coconut.
If the bitterness is still palpable, try salted coconut shreds (or salt them yourself by soaking in saline water).
cooking.stackexchange.com/users/27144/Epanoui
I'm making a salad that's quite bitter (endives, radicchio, arugula, with a lemon vinaigrette dressing). Normally this salad has peeled grana padano on top of it, which cuts the bitterness, but my co-diner can't have dairy (or gluten, sadly).   Any ideas for what I could add to a salad like this that would cut the bitterness similarly?  Thanks!
What's a good nondairy substitute for parmesan/grana padano as a salad-topper?
cooking.stackexchange.com
<salad><dairy-free>
cooking.stackexchange.com/questions/8179
cooking.stackexchange.com/users/2864/Ben Zotto
Try ham or bacon, marinated artichoke hearts or mushrooms, shredded coconut or a mixture of  baker's yeast, breadcrumbs, garlic powder, and salt. When using olives, try Graber or Castelveltrano. You can also use Sumak to cut some of the bitterness. You can try bacon, artichoke hearts, mushrooms or olives or sumak.
Try using bacon or parma ham. Artichoke hearts, mushrooms or olives would be a good choice. Try using sumak or shredded coconut.