Traditional versions of this sauce contain sugar, but we left it out for a more straightforward flavor. Serve with noodle bowls or rice dishes.
Heat oil in a medium saucepan over medium. Add chiles; cook 10 minutes, stirring often. Add vinegar and salt; cook 5 minutes, stirring occasionally.
Remove from heat; cool 10 minutes. Transfer mixture to a food processor; add 3 tablespoons water. Pulse until nearly smooth, 3 to 4 times. Serve immediately, or refrigerate in an airtight container up to 1 week.