Kim's Perfect Guacamole

Pile 1/4 cup chopped onion, 3 seeded & chopped serrano chiles, 3/4 cup torn cilantro, and a pinch of kosher salt on a cutting board. Chop and then slightly mash with the flat side of the knife. Transfer to a bowl, add 3 diced avocados and mash with a wooden spoon until combined but still chunky. Stir in 1 medium diced tomato and season with salt. Top with more tomato, cilantro, and onion (if desired). Serve with tortilla chips.