Heat oven to 375 F. Spray a 13x9-inch baking dish with nonstick spray.
Cook and drain manicotti according to package directions.
Cut each cheese stick in half lengthwise. Place one frank and one cheese stick half in each manicotti shell. Arrange in a baking dish. Spoon chili over manicotti; cover with foil.
Bake 45–55 minutes or until chili is bubbly and cheese is melted. Sprinkle onions over chili; drizzle with mustard.
