Cook the sweet pepper and onion in hot oil in a large skillet just until tender. Stir in the mangoes, brown sugar, vinegar, red pepper, and salt. Bring to boiling. Reduce heat and simmer, uncovered, about 10 minutes or until mangoes are tender. Cool slightly. Transfer mixture to a blender container or food processor bowl. Cover and blend or process until nearly smooth. Stir in the green onion.
To use, brush chicken, shrimp, fish, or pork with some of the sauce during the last 10 minutes of grilling. If desired, reheat and pass additional sauce. Cover and refrigerate remaining sauce up to 2 weeks. Makes about 2-1/2 cups (ten, 1/4-cup servings).