Is it ok to skip onions in a recipe?

While you can do whatever you want to recipes you're following, you should be aware that onions are the backbone of the flavor of many dishes. If the recipe calls for more than a quarter onion or so per serving, and particularly if they are to be browned rather than cooked until translucent, the dish will probably be blander than intended if you leave the onions out.

The good news is, there's a lot of things that are similar to onions, notably scallions, leeks and shallots (thanks Benjamin Hodgson). If you are more okay with any of these things, go ahead and substitute (in the case of scallions and shallots, the amount should be roughly halved).

You can absolutely leave the onions out! Onions are only necessary if you like them. And, no, you don't need to find a substitute.

Think about it this way. Recipes are like guides. You can tweak most recipes to your liking. That's one of the reasons you can find so many different recipes for the 'same' dish.

The only things that wouldn't be the same are onion based dishes, like perhaps French onion soup or an onion dip. But anyone who doesn't like onions probably wouldn't be making those - at least not for themselves.

If you don't like the flavour of any of the onion family, you'll have to be more creative. Some close replacements would be garlic, leeks or chives which are also related to onions, but may be just far enough away to replace some missing flavour (I won't go so far as to say substitute, as you'd sue smaller quantities).

If those are still too close, but you have a rather thin flavour overall, adding some finely chopped and well-browned carrot with a little celery and/or bell pepper can work in many dishes (such as Bolognese sauce, curry or chilli. Being a little generous with any herbs in the recipe also helps, as may a touch of sugar.

As onions have a thickening effect when cooked for long periods, a little less liquid overall might be a good idea.

You can edit out (omit) just about anything from most recipes I hate 'heat' in my food so I just leave out the chillies. Of course, it can significantly change the final flavours. So what? recipes are guidelines, and ver few need be followed exactly to still turn out a finished dish to my liking

Of course you can. As other have pointed out, a recipe is only for guidance. What I would like to add is, that far too many recipe books and cookery programs put too much emphasis on being precise in following recipes. The only important thing is whether you like the result, and the only way to find out by trying and accepting that you will fail from time to time. There are certain thing you shouldn't leave out - they are the "major components", like flour, if you bake a bread, or other things that constitute a large part of the recipe. Other than that, feel free - it's meant to be fun.

So, don't be afraid to experiment - the result may be surprisingly good; like banana and fish.

Remember that you can sauté an onion to have a sweetness to your dish without the onion taste.