In a large skillet, cook the beef, green pepper and onion over medium heat until meat is no longer pink; drain.
Stir in the pizza sauce, pepperoni, and oregano.
Spoon about 1/2 cup beef mixture off-center on each tortilla' top with a piece of string cheese.
Fold one side of tortilla over filling and roll up from the opposite side.
Place seam side down on an ungreased baking sheet. Bake at 350 for 10 minutes or until heated through and cheese is melted.
Wrap each roll-up in plastic wrap; place in a large freezer bag. Seal and freeze for up to 2 months.
TO USE FROZEN ROLL-UPS: Completely thaw in the refrigerator. Unwrap the roll-ups and place on a greased baking sheet. Spritz with cooking spray. Bake uncovered at 375 for 25-30 minutes or until heated through.