Preheat oven to 400°F.
Cut squash in half; scoop out and discard pulp and seeds. Slice squash into 1 inch thick slices.
Divide squash, mushrooms, and shallots among two baking sheets and drizzle with olive oil. Combine Poultry Seasoning, black pepper, and salt, then sprinkle over vegetables. Toss to coat.
Roast for 45 minutes or until squash is tender.
Top each pan with half the spinach and cook 1 more minute until spinach is wilted.