Preheat oven to 375°.
Wash squash; cut in half lengthwise. Remove and discard seeds. Place squash halves, cut side down, in a 13- x 9-inch baking dish. Add water to dish to depth of 1/2 inch. Cover and bake at 375° for 35 to 40 minutes or until squash in tender. Drain, and let cool slightly. Scoop out pulp, leaving 1/2-inch-thick shells. Reserve squash pulp for another use. Brush squash shells with honey; sprinkle evenly with cinnamon.
Bring apple cider and 1/2 cup water to a boil in a medium saucepan; add rice, apple, and cinnamon stick. Cover; reduce heat, and simmer 20 to 25 minutes or until liquid is absorbed and rice is tender. Remove and discard cinnamon stick.
Cook sausage and onion in a medium nonstick skillet over medium heat until sausage is browned, stirring until it crumbles. Drain and pat dry with paper towels.
Combine rice mixture, sausage mixture, mustard, and salt; stir well, Spoon mixture evenly into squash shells; place in baking dish. Bake at 375° for 20 minutes or until thoroughly heated.