This recipe is from Hugo Ortega’s Street Food of Mexico cookbook. Find several more recipes from the book here.

½ small white onion
2 garlic cloves, peeled
2 serrano peppers, roasted, peeled,
   stemmed 
½ small bunch cilantro, divided in half 
6 medium tomatoes, roasted, peeled 
1 ½ teaspoons kosher salt

Place onion and garlic in a food processor and pulse until finely chopped. Add peppers and half the cilantro and pulse 4 times. Add tomatoes and salt and pulse 4 times. Transfer to a bowl. Coarsely chop remaining cilantro and fold into the salsa.