Spray onion slices lightly with cooking spray. Place onion slices and chili peppers in center of grid over medium, ash-covered coals. Grill peppers and onion slices, covered, 11 to 15 minutes (over medium heat on preheated gas grill, 13 to 16 minutes) or until onion is tender and pepper skins are charred, turning occasionally. Place peppers in food-safe plastic bag; close bag. Let stand 15 minutes. Remove and discard skins, stems and seeds from peppers; cut into 1/2-inch slices.
Drain liquid from tomatoes into food processor or blender container; reserving tomatoes. Add onion, peppers, fish sauce, ginger, garlic and tomato paste to food processor. Pulse on and off until well blended.
Grate peel of lime; juice lime. Pour chili pepper mixture into medium saucepan; add reserved tomatoes, sugar, vinegar, lime peel and lime juice. Bring to a boil; reduce heat and simmer 1 hour or until thick and syrupy, stirring occasionally. Spoon off and discard any foam. Remove saucepan from heat; cool.
Nutrition information per serving: 552 Calories; 0 kcal Calories from fat; 0 g Total Fat; 0 g Saturated Fat; 0 g Monounsaturated Fat; 0 mg Cholesterol; 6.3 mg Sodium; 12 g Total Carbohydrate; 1 g Dietary Fiber; 2 g Protein; 0.6 mg Iron; 0.6 mg Niacin; 0.2 mg Vitamin B6; 0 mcg Vitamin B12; 0.2 mg Zinc; 0.6 mcg Selenium; 6.6 mg Choline;