Finely chop the onion so it blends smoothly into the guacamole without large visible pieces.
Seed the tomato and remove its juice. Cut it into small, fine dice.
Do the same for the chili pepper. Be careful not to rub your eyes afterward as it can sting. You may want to wear kitchen gloves.
Chop the cilantro more or less finely, according to your taste.
Cut the avocados in half and scoop out the flesh. Drizzle with lemon juice to prevent browning. Mash with a fork, leaving some larger chunks for a varied texture.
Add a bit of tomato, onion, chili, and cilantro. Mix and season with salt.
Taste and adjust the texture by adding more onion or other ingredients if needed.
You can add more lemon juice for a tangier guacamole and a couple of pinches of Espelette pepper or black pepper to enhance the flavor.
Serve preferably immediately after preparation with tortilla chips. Don’t skimp on the quality of the nachos.