How to make uncooked onion digestable? I have a problem with uncooked, sliced onion making me and other people feel uncomfortable in the stomach, sometimes whole night. However, when I eat tacos out in restaurants that never happens. Is it due to the variety of onion or do they prepare them in a certain way?
Adding salt and lemon should do it, or at least help a lot.

What you want to do is to chop them up and rub in a little salt and a splash of lemon juice (vinegar should work too). Obviously you don't want to add so much of either that you won't want to eat the onion.
Leave to sit in the fridge overnight and enjoy.