Cut avocadoes in half. Remove the pits. Score the flesh. Scoop it out with a spoon into a big bowl.
Mash avocado roughly with a fork. (Do not overdo - should be a little chunky.)
Sprinkle salt and lemon juice.
Chop the red onion and add 4 tbsp in.
Add grated black pepper.
Chop the tomato and add it just before serving.
Open the bag of tortilla chips for serving.
If making in advance, place plastic wrap on the guacamole surface and press down to cover (to prevent air from reaching it and causing oxidation). Refrigerate until ready to serve.