Cut the avocado in half. Remove the seed and scoop out the jelly.
In a large bowl, use a fork to crush the avocado jelly. You can keep some larger pieces if you prefer.
Add the onion, lime juice, salt and pepper, and mix for 1 minute so that the seasoning can dissolve and spread evenly throughout the avocado to make a nicely blended guacamole.
Optional: add tomatoes and mix.
Serve cold. Store in the fridge in a tightly sealed container to about 3 days.