How to Make It
Preheat grill to medium-high heat.
Combine onion and bell pepper in a bowl. Bring 1/2 cup vinegar, 1/2 cup water, sugar, and 1 tablespoon salt to a boil in a small saucepan over medium-high heat. Pour vinegar mixture over bell pepper mixture; let stand 15 minutes. Drain.
Bring remaining 1/4 cup vinegar, remaining 1/4 cup water, 1/4 teaspoon salt, ketchup, and next 6 ingredients (through red pepper) to a boil in a saucepan over medium-high heat. Cook 4 minutes or until slightly thickened, stirring occasionally. Place 1/2 cup sauce in a small bowl; reserve.
Coat grill rack with cooking spray. Sprinkle pork with remaining 1/2 teaspoon salt. Add pork to grill; grill 10 minutes, turning occasionally. Brush pork with remaining sauce; grill 5 minutes or until a thermometer inserted in the center registers 140°. Place pork on a cutting board; let stand 5 minutes. Cut into 12 slices. Serve with bell pepper mixture and reserved 1/2 cup barbecue sauce.