I use a food processor for this recipe. Chop the peppers, onions, and cilantro (no stems); add them along with the whole jar of garlic and oil to the food processor; blend them together until it's a thick mixture. Everything should be chopped and blended, no large chunks.
This can be stored in the refrigerator and used as needed. If your batch comes out pretty large you may want to divide it and freeze half.