Preheat the oven to 400ºF. Line 2 baking sheets with parchment paper. Place the squash halves cut sides up on the baking sheets. Brush with 4 tablespoons of olive oil. Sprinkle with salt and pepper. Bake for 45-55 minutes, until tender when pierced with a fork.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the turkey. Cook, breaking up with a wooden utensil, until cooked through and no longer pink. Transfer to a large bowl. Add the remaining 2 tablespoons of oil to the pan. Add the apples, onion, celery, and mushrooms. Cook, stirring occasionally, for 5-6 minutes. Add the garlic and poultry seasoning and stir for 1-2 minutes. Transfer the mixture to the bowl with the turkey. Stir to combine, then taste and season with salt and pepper, if desired. Stir in the almond flour and egg whites.

When the squash halves are finished roasting, pile the stuffing evenly into the halves. Return to the oven for 15 minutes. Serve warm.