Step 1 In a molcajete, grind together the onions, chiles, chopped cilantro and salt to a paste.
Step 2 Cut the avocados into halves, remove the pits and spoon the flesh into the molcajete. Mash the avocado into the onion-chile mixture until it is a uniform texture, but not smooth (it should still have some lumps).
Step 3Stir in the tomatoes and lime juice, adjust the seasoning and top with the cilantro leaves.