Place a baking sheet on the middle oven rack and preheat to 475 degrees F. Toss the squash in a large bowl with the melted butter and season with salt and pepper. Spread out on the hot baking sheet and roast until tender and browned, about 45 minutes.
Meanwhile, combine the pomegranate juice, maple syrup, vinegar, chile powder, garlic and 1/4 teaspoon salt in a small saucepan. Bring to a boil, then reduce the heat and simmer until reduced to about 1/3 cup, 15 to 20 minutes. Discard the garlic.
Arrange the squash on a platter. Drizzle with the pomegranate glaze and top with the parsley.
Slice the squash 1 day ahead; refrigerate in a resealable plastic bag. Make the glaze (step 2) up to 1 day ahead and refrigerate; reheat in the microwave in 10- to 15-second intervals.