Cut the avocado in half and remove the core. Remove the pulp from the skin and place in a bowl. Add the avocado seeds (this will prevent the avocado from turning black so quickly).
Cut the tomato and onion into small cubes and add. Add the lime juice and salt and stir everything well.
You can also mix in 30 g of cilantro and a fresh, raw, finely chopped chilli pepper (jalapeño or cerrano) if desired.