Add avocados, red onion, jalapeño peppers, lime juice, 3 tablespoons of water, garlic, red pepper flakes, kosher salt, and black pepper to the bowl of a food processor.
Pulse until everything is well blended, stopping to scrape down the sides of the bowl as needed. If the mixture is too thick, add more water, one tablespoon at a time, until you reach your desired consistency.
Transfer the mixture to a bowl and stir in the chopped cilantro.
Serve immediately with tortilla chips, spooned over tacos, or as a dip for nachos.