Chop into small pieces. (I try to make them about 1/4" so they're easy to scoop up on a chip.) Place in a bowl large enough to hold all ingredients.
Chop onion into approximately the same size pieces as your tomatoes. Place in bowl.
Add remaining ingredients and stir to combine. Add more or less depending on your taste preference. You can use lemon juice instead of lime juice if you prefer. Refrigerate for at least an hour before serving with chips, scoops or use as a topping for salad, tacos, etc.