Preheat oven to 400°F. Season squash with salt and pepper, arrange cut side up in a 9-by-13-inch baking pan, cover tightly with aluminum foil and bake until tender when pierced with a fork, 45 minutes. Sprinkle squash with brown sugar and bake, uncovered, for 20 minutes, or until edges are browned.
Arrange squash on a serving platter; spoon any melted sugar from pan onto squash. (If sugar has hardened, add 1 Tbsp. water to loosen.) Serve hot.