Preheat your oven to 375°F (190°C).
Cut the acorn squashes in half lengthwise and scoop out the seeds.
Brush the flesh of the squashes with olive oil and sprinkle with a pinch of salt. Place them on a baking sheet, flesh-side down, and bake for 30-35 minutes, or until the flesh is tender when pierced with a fork.
While the squashes are baking, prepare the stuffing. In a large skillet, heat olive oil over medium heat.
Add the diced apple, onion, and celery. Sauté until the vegetables are softened and the apples are slightly caramelized, about 5-7 minutes.
Stir in the raisins, ground cinnamon, ground nutmeg, ground sage, salt, and pepper. Cook for an additional 2 minutes, allowing the flavors to meld.
Remove the skillet from heat and fold in the cooked quinoa, chopped walnuts, and fresh parsley. Mix well to combine.
Once the squashes are tender, carefully flip them over on the baking sheet, flesh-side up.
Divide the stuffing mixture among the squash halves, gently pressing it down.
If using, sprinkle grated Parmesan cheese over the stuffed squashes.
Return the baking sheet to the oven and bake for an additional 20-25 minutes, until the stuffing is heated through and the cheese is melted and golden.
Remove from the oven and let them cool slightly before serving.
Drizzle with honey for a delightful touch of sweetness, if desired.