Halve the avocados with a sharp knife, remove the stones and scoop the flesh into a medium bowl. Using a fork, mash the avocado flesh to the desired texture (chunky or smoother as you prefer).
Halve the lime or lemon and juice with a citrus juicer. Add 1 Tablespoon of juice to the avocado and stir to combine.
Peel the garlic clove and finely mince. Peel and finely dice the red onion. Halve the chilli and remove the seeds with a knife. Dice the tomatoes. Finely chop the coriander (cilantro) leaves.
Add all of the additional ingredients to the avocado mixture and stir to combine.
Spoon guacamole into a serving bowl and garnish with coriander (cilantro) leaves.