Cut steak across the grain into bite-size strips. Add oil to a 12-inch skillet; preheat over medium-high heat. Stir-fry meat and green pepper for 2 to 3 minutes or until meat is done. Remove from heat. Drain if necessary. Toss with salad dressing.
Fill each pita half with some of the meat mixture. Top with cheese. Serve with salsa or taco sauce. Makes 4 servings.