Invert squash in an 11-in. x 7-in. baking dish. Add water and cover with foil. Bake at 375° for 50-60 minutes or until tender.
Meanwhile, cook beef, onion and celery over medium heat until no longer pink; drain. Stir in the flour, salt and sage until blended. Add milk. Bring to a boil. Cook and stir for 2 minutes or until thickened and bubbly. Stir in rice.
Transfer squash to a baking sheet. Fill cavity with meat mixture. Bake at 350° for 30 minutes. Remove from oven; sprinkle with cheese and bake 3-5 minutes longer or until cheese is melted. Yield: 4 servings.