Prep: 1. Chop: jalapeño chiles, green onions, sweet onion, and cilantro. Make: 1. Combine jalapeño chiles, green onions, sweet onion, and cilantro in processor; purée until paste forms, scraping down sides of bowl with rubber spatula several times. 2. Add 2 tablespoons vinegar and process until mixture is blended but some texture still remains. Transfer to bowl. 3. Stir in 3/4 teaspoon coarse salt, 1/4 teaspoon pepper, and more vinegar to taste, if desired. DO AHEAD: Can be made 1 day ahead. Cover and refrigerate.
Goes well with steak!