A lot of veggies take some preparation and blanching to freeze, but all you need to do for onions and peppers is clean, chop and freeze. I use a lot of both in my cooking and having them ready to use can save a lot of time. You don't have to do large batches (unless you've found a really good bargain), there's been times I've used half a pepper for a recipe and froze the rest.
Doing it this way keeps them from sticking together in one big clump so you can remove the quantity needed. The procedure is fairly simple:
1. Peel onions and clean and seed the peppers
2. Slice or dice them as you would for different recipes
3. Spread out on a cookie sheet
4. Place in freezer until frozen
5. Then place in bag or container and return to freezer until needed