Wash and dry the cilantro and lime. Halve the avocados lengthwise, remove pits, and scoop flesh into a medium mixing bowl. Seed the tomato (cut a small X at the stem end and squeeze out seeds or scoop with a spoon) then finely dice. Finely mince the white onion. Cut the jalapeño in half, remove seeds and membranes if you want milder heat, then finely mince. Chop the cilantro leaves and tender stems finely. Juice the limes until you have about 2 tablespoons of juice.

Mash and combine

Using a fork or a potato masher, coarsely mash the avocado in the bowl — leave some small chunks for texture. Immediately add the lime juice and kosher salt and mix to combine (the acid helps slow browning). Add the minced onion, diced tomato, minced jalapeño, and chopped cilantro to the bowl. Gently fold together until evenly distributed. If using, stir in the olive oil and ground cumin.

Season and adjust

Taste the guacamole and add more salt, lime juice, or jalapeño to adjust seasoning and heat. Add the freshly ground black pepper and stir. Aim for a bright, balanced flavor: lime to brighten, salt to enhance, cilantro and onion for freshness, and jalapeño for heat.

Rest and serve

If not serving immediately, press a piece of plastic wrap directly onto the surface of the guacamole to minimize air contact and refrigerate for up to 24 hours (best within a few hours). When ready to serve, transfer to a serving bowl, garnish with a few cilantro leaves or a light drizzle of olive oil if desired, and serve with tortilla chips or warm tortillas.