Question: For me it seems that in the following case expression seems not to be fitting, I think the second example is shorter, simpler and may even be more correct.

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2. dugite - Elegant bindings to work with Git in your Node applications

Answer: 
If one says "I ate out on Monday" it necessarily implies the nearest previous Monday. 

"Last Monday" generally implies "Monday of last week". For example, if today were Tuesday or Wednesday and someone said "I ate out last Monday", almost no one would wonder if they meant yesterday. But as days pass, particularly towards the end of the week and especially on the weekend, that difference becomes more muddled.
So I'd say if a Monday had past since you ate out, then I suppose you would say "I Ate Out Last Monday."
If, say its the next day, so Tuesday. "I ate out on Monday," Would be what you want to say.