Toss steak slices with Seasoning and oregano in medium bowl. Set aside. Heat oil in large skillet on medium-high heat. Add bell pepper and onion; cook and stir 5 minutes. Remove vegetable mixture from skillet.
Stir beef mixture into skillet; cook and stir 5 minutes or until beef is no longer pink. Return vegetable mixture to skillet; cook and stir 1 to 2 minutes or until heated through.
Spoon onto warmed tortillas. Serve with assorted toppings, if desired.