Cut the avocados in half and remove the pits. Scoop out the avocado flesh into a mixing bowl.
Use a fork or potato masher to mash the avocados to your desired consistency. Some people prefer it chunky, while others like it smooth.
Add the finely diced red onion, diced tomatoes, minced garlic, and chopped jalapeño (if using) to the mashed avocados.
Stir in the chopped cilantro and squeeze the juice of 1-2 limes over the mixture. Lime juice adds a bright, citrusy flavor and helps prevent the avocados from browning.
Season the guacamole with salt and pepper to taste. Start with a pinch of salt and adjust according to your preference. Gently mix all the ingredients together until well combined.
Taste the guacamole and adjust the lime juice, salt, or pepper if needed. Customize the flavor to suit your taste buds.
Transfer the guacamole to a serving bowl. If not serving immediately, press plastic wrap directly onto the surface of the guacamole to minimize browning.