In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in salsa and taco seasoning. Bring to a boil. Reduce heat; simmer, uncovered, for 2-3 minutes. Transfer to a large bowl; set aside., In a food processor, combine pinto beans and water. Cover and process until almost smooth. Add to beef mixture. Stir in cheese. , Spoon 1/2 cup beef mixture down the center of each tortilla. Fold ends and sides over filling; roll up. Wrap each burrito in waxed paper and foil. Freeze for up to 1 month., To use frozen burritos: Remove foil and waxed paper. Place one burrito on a microwave-safe plate. Microwave on high for 2-1/2 to 2-3/4 minutes or until a thermometer reads 165°, turning burrito over once. Let stand for 20 seconds.