Take a large frying pan and place it on your stove at medium heat
Cut each pepper and tomatillo in half and place the skin side down on the frying pan. Allow to cook until slightly charred. It is important that you DO NOT remove any seeds.
Place all the charred vegetables in a food processor or hand chopper
Pulse a few times. Do not over chop at this point.
Add cilantro, white onion, garlic & salt into the food processor. Pulse a few more times.
Add avocado if using.
Pulse a few more times until you get your desired salsa consistency.