Slice the onion into thick slices and add them to a large bowl of cold water. Allow them to soak while you prepare the rest of the ingredients.

Peel and pit the avocados and add them to a large mixing bowl. Use a fork or pastry cutter to mash the avocados to your desired consistency.

Dice the jalapeño and tomatoes, removing the inner membranes and seeds from the jalapeño.

Drain the onion slices and dice them into small pieces. Add the diced onion, jalapeño, tomatoes, garlic, lime juice, sea salt, and black pepper to the mashed avocado and stir to combine.

Fold in the chopped cilantro. Serve.