Mix batter ingredients in a pre-sprayed 9-1/2-inch deep dish pie plate. Heat olive oil in skillet over medium heat. Add onions and peppers, if desired, and cook until softened. Stir in chopped roast beef and remove from heat.
Top batter with roast beef mixture. Using fingers or spoon; firmly push topping into dough; Arrange cheese slices evenly over meat.
Bake by placing in a COLD oven; set temperature to 350°F. Bake for 30 minutes or until done.