Preheat the oven to 425°. Put the squash wedges on a large, rimmed baking sheet and brush all over with 2 tablespoons of the melted butter. Season with salt and pepper and scatter 4 of the thyme sprigs on top. Bake in the upper third of the oven for about 25 minutes, or until just tender. When cool enough to handle, peel the squash and cut the flesh into 1-inch dice. Transfer to a large baking dish.