Soak the onion in cold water for 15 minutes. Drain and transfer to a large bowl.

On a cutting board, lightly sprinkle the garlic with a pinch of salt and smash it into a paste with the side of a cook's knife. Transfer the paste to the bowl with the onion.

Using a knife cut the avocados in half, rotating around the seeds. Remove the seeds and discard (See Cook's Note.). Using the knife, carefully make several slashes in the avocado flesh. Using a spoon, scoop the avocado flesh into the bowl with the onion and garlic. Repeat with the remaining avocados.

Add the coriander, tomato, and jalapeno, to taste, to the avocados. Using a rubber spatula or large fork, mix until just combined, keeping the guacamole chunky. Season with salt, to taste. Serve immediately.

Cook's Note: Here's a quick and easy and way to remove the seed from an avocado: tap the edge of a cook's knife into the seed and twist--the seed will pop out. Knock the knife on the edge of a counter and the seed will drop off.