Cut ripe avocados in half lengthwise, remove pits, and scoop flesh into a bowl
Mash avocados with a fork until mostly smooth or to your preferred texture
Add diced onion
Add minced garlic
Add chopped cilantro
Add diced tomatoes (optional)
Squeeze in fresh lime juice
Add salt to taste
Add diced jalapeño or serrano (optional)
Add black pepper to taste
Stir until evenly combined
Taste and adjust salt, lime juice, and heat as needed
Serve immediately or cover and press plastic wrap directly on the surface to reduce browning