In a large mixing bowl, combine the cilantro, jalapeño, onion, 2 tablespoons of lime juice, garlic, salt, pepper, cumin, and cayenne.
Cut one avocado in half, remove the pit, scoop out the flesh with a large spoon and add to the bowl with the spices. Using a fork, mash the avocado until mostly smooth and combined with the onion mixture.
Halve the remaining two avocados, remove the pits then carefully make ½-inch crosshatch cuts in the flesh with a table knife. Cut all the way through the flesh but not through the skin. Using a large spoon, carefully scoop out the avocado cubes and add to the mashed mixture.
Sprinkle the remaining 1 tablespoon lime juice on top of the cubes. Using a rubber spatula, fold the cubes into the mashed mixture taking care to leave the guacamole somewhat chunky. Check the seasoning and adjust if needed.
Transfer to a serving dish and garnish with extra chopped red onion, cilantro leaves and chopped tomatoes if desired.