Cut the avocados in half and take out the stones. With a spoon, remove the avocados from their skin and place in a bowl. Mash the avocados with a fork until they are mostly smooth but leave some chunks.
Finely chop the onion and add to avocado mix. Chop the tomatoes in small pieces and add them to the mix. Squeeze the lime and add a bit of salt and pepper. Mix carefully, trying not to crush the tomatoes. Serve with tortilla chips, or add to fajitas, tacos, or your favorite dish.
Notes
You can add heat to your guacamole by throwing in a fresh jalapeno pepper. Chop it finely, and consider whether you want to keep or discard the seeds, since they can be very hot.