Using the “pulse” button in your blender or food processor mix the tomatillos, onion, serranos, half of the avocado and half of the cilantro to a rough texture. We want to imitate a rustic salsa out of a molcajete. Place the mix on a bowl. Cut the rest of the avocado into small cubes and rough chop the cilantro, and throw both on top of the salsa.