Preheat oven to 400°F.
Halve squash and remove seeds. Slice into thin (1/2-inch thick) half moons. Pile squash on a rimmed, nonstick baking sheet and drizzle with about 2 tablespoons EVOO. Season it with salt, pepper and nutmeg. Toss squash to coat and arrange in even layer.
In a large mixing bowl, combine mustard and syrup. Add 4 cloves chopped or grated garlic, a fat drizzle of EVOO, about 2 tablespoons, and rosemary. Season chicken with salt and pepper, add to bowl and toss to coat evenly. Arrange chicken over the squash in even layer, roast to an internal temperature of 165°F and deeply golden and glazed, about 35-40 minutes.
Serve chicken with squash alongside.