Basic guacamole is spiced up with serrano chiles; if you prefer it less spicy, remove the ribs and seeds from the peppers.
In a large bowl, mix together the onion, chiles, 2 tablespoons of cilantro, and salt.
Crush the avocados into the onion mixture, leaving the mixture chunky.
Fold in the tomatoes. Sprinkle over remaining cilantro. Serve with tortilla chips or other toasty corn product.