Cut the avocado in half, remove the pit, and scoop out the middle, leaving a margin inside about 0.2 - 0.4 inches thick. Dice the avocado flesh as well. Quarter the tomatoes and chop the onion.

Cut the avocado in half, remove the pit, and scoop out the middle, leaving a margin inside about 1/2 - 1 centimetre thick. Dice the avocado flesh as well. Quarter the tomatoes and chop the onion.