Wash the tomato and cilantro, and chop them.
Chop the onion.
Cut the lime in two.
With the same knife, split the avocados in half, leaving the pit in there. Remove the pit, and scoop the flesh of the avocado with a spoon to a bowl. Reserve one of the pits.
Mash the avocados with a fork, mixing them with the salt and olive oil.
Mix in the cilantro, onion and tomato.
Squeeze the lime over the guacamole, and mix thoroughly.
Put the pit you reserved in the guacamole. Rumor has it that it prevents it from turning brown. I have no scientific proof of that, but since it doesn't hurt, and it adds the hippie touch, I keep doing it.