Slice steak across the grain in 2 by 1/4 inch strips. Place in zipper-locking plastic bag. Combine lime juice and oil; pour over steak strips. Marinate in refrigerator for 30 minutes. Remove steak strips from marinade; discard marinade. Sprinkle fajita seasoning on steak strips. Spray skillet with vegetable spray. Sauté beef over high heat, stirring constantly until brown, about 3 to 5 minutes. Add onion and pepper strips and continue stir-frying until most of liquid is absorbed and onions are slightly brown, about 10 minutes. Serve immediately in flour tortilla with choice of grated cheese, salsa, guacamole and sour cream condiments.