Lightly crush the chopped onions, cilantro, jalapeno, salt, & juice from 1 lime. If you do not have a molcajete (mortar and pestle), you can use a mixing bowl and a fork.
Add roughly chopped avocado.
Mash to your desired consistency. You can make it smooth if you prefer, but authentic guacamole has a chunky texture.
Gently fold in chopped tomato. Taste & adjust for salt and lime, then serve and enjoy :)
Notes
Choosing between red and white onion: Use red onion if you prefer a milder flavor that is slightly sweet. Use white onion for a sharper bite. I prefer red, but white is more traditional
If making for a party or dinner guests: Consider putting the cilantro on the side, or making one bowl with cilantro and one without. Some people have a genetic aversion to cilantro, and your guests will appreciate your thoughtfulness!
Storage: Guacamole is best served fresh, but it can keep in the fridge for no more than 2 days if stored properly!