
Preheat the oven to 400°F. Peel the carrots, then cut them in half lengthwise and crosswise.
Peel the butternut squash and cut it into cubes.
In a large bowl, toss the squash and carrots with the brown sugar, olive oil, salt, cinnamon and nutmeg until all the vegetables are evenly coated.
Transfer the vegetables to two greased, foil-lined 15x10x1-inch baking pans, spreading them out in a single layer to ensure even roasting. Roast the vegetables for 30 minutes, stirring them occasionally to promote even cooking and browning.
After 30 minutes, sprinkle the chopped walnuts evenly over the vegetables, then roast the pan for 5 to 10 minutes longer, or until the vegetables are tender when pierced with a fork.