In a bowl, combine jalapeño, cilantro, salt, lime juice and garlic, if using.
Just before serving, cut avocados in half. Remove pits. Scoop out flesh and dice. Add to mixture in bowl and mash with a potato masher. Guacamole can be as smooth or chunky as you wish. Taste and adjust seasonings.If not serving immediately, cover surface of guacamole directly with plastic wrap to help prevent discolouration. (Lots of lime juice also does the trick.)