Mix marinade, ketchup, sesame seed and red pepper in small bowl. Reserve 2 tablespoons marinade for brushing.
Place steak in large resealable plastic bag. Add remaining marinade mixture; turn to coat well. Massage steak and marinade for 5 minutes. Remove steak from marinade. Discard any remaining marinade.
Grill steak over medium-high heat 7 to 8 minutes per side or until desired doneness, brushing with reserved marinade mixture. Discard any remaining marinade. Grill peach slices 1 to 2 minutes per side or until lightly browned. Cut steak across the grain into thin slices. Serve with grilled peaches.