1. Preheat oven to 375°.
2. Cut butternut squash in half and scoop out seeds. Brush with oil and season generously with salt and pepper. Place squash cut-side down on a large parchment-lined baking sheet. Bake until soft and tender, about 45 minutes.
3. While squash is baking, cook sausage in a large skillet over medium-high heat until golden-brown and cooked through, about 8 minutes. Use a slotted spoon to transfer cooked sausage to a bowl. Reduce heat to medium and add shallots to skillet; cook until softened, 3–4 minutes. Add mushrooms, herbs de Provence, and garlic and continue cooking until fragrant, about 2 minutes. Transfer shallot mixture to bowl with sausage.
4. Add wine to skillet and use a wooden spoon to scrape up any brown bits from bottom of pan. Reduce wine until almost evaporated, then add spinach and stir until wilted. Transfer spinach to sausage mixture. Add ½ cup grated cheese to sausage mixture and stir to mix well. Set mixture aside.
5. Remove squash from oven and when cool enough to handle, scoop out a bit of flesh to make space for filling. Stuff squash halves with sausage mixture and sprinkle with remaining ½ cup cheese. Return to oven and bake until cheese is melted, about 10 minutes. Serve hot.