Slice avocados in half, remove pits, and scoop avocado flesh into medium mixing bowl. Add tomato, onion, and cilantro to bowl with avocado. Mash and mix well. Add lime juice, salt and pepper. Mix again and serve.
Store the guacamole in a sealed container in the refrigerator for up to 2 days. Or store in a bowl covered with plastic wrap. Press the plastic wrap down so that it is flush with the bowl to prevent the guacamole from browning.