Add the tomatillos, jalapeños or serrano chiles, cilantro, garlic, and onion to a food processor or blender and pulse until chunky but not pureed.

Cut the avocado in half, remove the pit, score the flesh lightly, and scoop into the processor.

Add lime juice and salt, then stir by hand to combine, keeping the avocado chunky.

Taste and adjust seasoning as needed, then serve immediately or refrigerate for up to 2 days.