To make the guacamole, cut the avocados in half. Remove the pit. Slice the avocado with a knife while it's still in the skin. Scoop out avocado from the peel, put in a large bowl. Using a fork, mash the avocado. Add the onion, garlic, jalapeño, cilantro, lime juice, tomato, salt and pepper. Stir gently until well combined.