Place beef in resealable food-storage plastic bag. In small bowl, combine taco seasoning mix, brown sugar, lime juice and pepper sauce. Pour over beef; seal bag. Let stand 15 minutes.
Spray grill pan with cooking spray; heat over medium-high heat. Remove beef from marinade. Place beef in pan. Cook 8 to 10 minutes, turning once, until desired doneness. Remove from pan to cutting board; let stand 5 minutes.
Meanwhile, in grill pan, cook bell pepper and onion 5 minutes, stirring occasionally, until vegetables are tender and browned.
Cut steak across grain into thin slices. To serve, place beef and vegetables evenly down center of warmed tortillas. Add desired toppings. Roll tortilla around filling.