Invert squash in a greased 15" x 10" x 1" baking pan. Bake at 350 degrees, uncovered, for 35-45 minutes or until tender. While squash is baking, cook beef, onion and garlic, in skillet, until meat is brown and onion is tender. Drain. Pour beef stock in skillet. Stir in remaining ingredients. Turn squash cut side up in pan and fill with mixture. Fill pan with hot water 1/4 inch; cover loosely with foil.