Place chicken in baking pan. Season with salt and pepper. Place mustard in small bowl. Whisk in orange juice, oil and pepper flakes. Pour over chicken, turning chicken to coat. Let stand 20 minutes. Combine chili sauce and hoisin sauce in small bowl. Prepare barbecue (medium-high) or preheat broiler. Grill chicken until just cooked through, about 10 minutes per side. Brush one side with chili-sauce mixture and grill until beginning to brown, about 3 minutes. Brush second side with sauce and grill until beginning to brown. Serve hot.