Place avocado in a medium bowl and mash a little. When you mix all of the ingredients together it will break up even more, so if you like chunky guacamole don't mash it up too much to begin with.
Add onion, garlic, cilantro, jalapeno, tomatoes, lime, salt and pepper and stir. Taste for seasoning.
Let stand in the refrigerator, or at room temperature, for 1 hour.
Recipe by Not Just Sunday Dinner at https://notjustsundaydinner.com/guacamole/