Preheat oven to 350°. In a large skillet, cook and crumble beef with pepper and onion over medium-high heat until no longer pink, 5-7 minutes; drain. Stir in pizza sauce, pepperoni and oregano. , Spoon 1/2 cup mixture across center of each tortilla; top with a piece of string cheese. Fold bottom and sides of tortilla over filling and roll up. , Place on an ungreased baking sheet, seam side down. Bake until heated through, about 10 minutes. Freeze option: Cool beef mixture before assembly. Individually wrap roll-ups in foil and freeze in a freezer container. To use, partially thaw overnight in refrigerator. Reheat foil-wrapped roll-ups on a baking sheet in a preheated 350° oven until heated through. To reheat individually, remove foil and rewrap in paper towel; place on a microwave-safe plate. Microwave on high until heated through, turning once. Let stand 15 seconds.