Place the jalapeno and garlic in the molcajete if using or in a shallow bowl and add a pinch of salt. Mash the garlic and jalapeno with the salt to make a paste.
Add the onion and mash a little but don't completely break up. Add the avocado and combine. Add your lemon juice, stir and check your seasoning. Add salt and pepper as needed.
Add your diced tomatoes and chopped cilantro. Serve immediately or store in an airtight container in the refrigerator. I find that a container that doesn't leave too much room after your guacamole works the best or keeps it from getting brown on top quicker. Enjoy!
