If desired, partially freeze beef for easier slicing. If using steak, trim fat from meat. Cut beef or chicken into bite-size strips.
Wrap tortillas tightly in foil. Heat in a 350 degree F oven about 10 minutes or until heated through. Meanwhile, heat oil in a 12-inch skillet over medium-high heat. Add meat, onion, and green pepper; cook and stir for 2 to 3 minutes or until desired doneness for steak or until chicken is no longer pink. Remove from heat. Drain well. Stir in tomato and salad dressing.
To serve, fill warm tortillas with meat mixture. Roll up tortillas. Serve with cheese, salsa and, if desired, sour cream. Makes 4 servings.