Dice onion, tomatoes, and avocados, adding to a large bowl.
Squeeze the juice of one lemon over salad for flavor and to keep the avocado fresh and green.
Add 1/4 tsp. pepper (or more to taste) and the chopped cilantro.
Mix in the olive oil until all the ingredients are lightly coated.
Feel free to add more olive oil if needed.
Cover and chill for at least one hour for best flavor.