2 tablespoons finely chopped white onion
1 tablespoon minced fresh serrano or jalapeno chile, including seeds, or more to taste
1/2 teaspoon kosher salt, or 1/4 teaspoon fine salt
1/4 cup chopped coriander, divided
1 large or 2 small ripe avocados, halved and pitted
A squeeze of lime, if desired
Mash the onion, chile, salt (the coarseness of kosher salt helps you make the paste), and half of the coriander to a paste in a molcajete or other mortar. You can also mince and mash the ingredients together on a cutting board with a large knife or a fork, and then transfer the paste to a bowl.
Score the flesh in the avocado halves in a crosshatch pattern (not through the skin) with a knife and then scoop it with a spoon into the mortar or bowl. Toss well (it should be like salad properly dressed in vinaigrette), then add the rest of the coriander and mash very coarsely with a pestle or a fork. Season to taste with lime juice (if you'd like) and additional chile and salt.