Optional: Roast jalapenos by holding them with tongs over a burner flame until skin blackens. Peel skins off, using gloves or holding a paper towel between your skin and the peppers.
Chop peppers and place in a strainer with a small saucepan underneath to catch juices.
Chop tomatoes, tomatillos, and onion, collecting all juices, and put in colander.