Preheat oven to 400F. Cut acorn squash into halves and scoop out the seeds and fibers. Place the halves, cut side down, in a baking dish. Add water to a depth of about 1/4 inch and bake for 30 minutes or until the squash is just tender.
While the squash is baking, brown the ground turkey in a large skillet over medium-high heat. Once cooked, reduce heat to low. Add salt, rosemary, cinnamon, and sage. Stir until well combined.
Add onion, apples, and raisins to turkey mixture. Remove from heat.
Once the squash is tender, remove from the oven and immediately turn the squash so the cut sides are facing up. Drain any liquid from the baking dish. Scoop the pulp out of the shells, leaving about 1/4 inch wall of squash around each shell.
Mash the pulp with the back of a fork and combine with the turkey mixture.
Place the mixture into the hollowed out squash shells and return to the oven for 20 to 30 minutes or until the apples are tender.
Garnish with fresh sage and serve warm.