If you need to use chopped onions in a dish that is not going to be baked long enough for the onions to get cooked, put the chopped onion in a bowl with about 1 tbsp olive oil and microwave covered for 30 - 60s (depending on how soft you'd like them). Then add them to the rest of the ingredients. This also works for green/red/yellow sweet peppers. E.g. if you're making an omelet, put chopped onion and green pepper in a bowl with 1-2 tbsp olive oil (depending on the volume), microwave for 1 minute before adding to the rest of the omelet topping.
If you want to add onion rings to salad though but don't like that sharp, bitter taste, put the chopped onion in a bowl, just cover with boiling water and let stand for 1 - 2 minutes. Drain well and then add to rest of salad ingredients.