Heat oil in a medium saucepan over medium heat. Add onion and ginger to hot oil; cook and stir occasionally for 1 minute. Add peaches, soy sauce, honey, vinegar, and fish sauce. Heat to a simmer and cook, uncovered, for 10 to 15 minutes or until peaches soften and begin to break down, stirring occasionally. If desired, sprinkle with crushed red pepper. Serve with grilled meat or crusty bread.
Store any remaining sauce in an air tight container in the refrigerator for up to 5 days.