Make several deep slits in the turkey; insert a garlic slice into each slit. Combine the oregano, lemon juice, salt and pepper; rub over turkey. Place flour in oven bag and shake well. Place turkey in bag and close. Refrigerate for 6 hours or overnight.
Place oven bag in a roasting pan at least 2 in. deep. Add onions, potatoes and carrots to bag. Close bag with nylon tie provided (do not allow oven bag to hang over pan). Bake, uncovered, at 350° for 2-1/2 to 3 hours or until thermometer reads 180°. Remove turkey from bag. Let stand for 20 minutes before carving. Keep vegetables warm. Serve turkey and vegetables with drippings.