Preheat the oven: Set to 400°F (200°C) and line a baking sheet with parchment paper.
Prepare the squash: Cut acorn squashes in half, remove seeds, and score the flesh lightly. Place cut-side up on the baking sheet.
Season the squash: Brush with melted butter (or olive oil), sprinkle with salt, pepper, cinnamon, nutmeg, and allspice.
Roast the squash halves: Bake for 30-35 minutes until tender and slightly caramelized.
Prepare the filling: Mix cranberries, walnuts, maple syrup, and a pinch of cinnamon in a bowl. Add brown sugar if desired.
Fill the squash: Spoon the cranberry-walnut mixture into the center of each squash half.
Bake again: Return to the oven and bake for 10-15 minutes until cranberries soften and walnuts are toasted.
Garnish and serve: Sprinkle with parsley or feta (if using) and serve warm.