Preheat oven to 325 degrees. Shake flour in oven bag. Place in 9x13x2 inch baking dish. Add barbecue sauce, onion, and green pepper. Squeeze bag to blend ingredients. Cut ribs into serving-size pieces (single or double ribs, depending on amount of meat). Place ribs in bag, and turn bag to coat ribs. Arrange ribs in even layers in the bag/baking dish. Close bag with a metal tie (not plastic). Cut six 1/2-inch slits in the top of the bag. Bake 1-1/2 hours or until tender. Makes 4 to 6 servings.