Chop the tomatoes and cucumber into small chunks and finely chop the red onion. Chop the cilantro as well. Chop the avocado last and be sure to have your lemon juice and olive oil ready to cover so the avocado doesn't brown. 1 lemon should give you 2 tablespoons of lemon juice. Add salt and pepper, toss a few times and serve!
You can adjust the ingredients however you like or add a few of them. You can use different types of tomatoes and you also don't need to use too much red onion as it can make it a bit harsh.