Preheat oven to 400 F. Start by roasting the squash. Slice in half lengthwise and scoop out the seeds. Lightly spread the olive oil around the cut rims of the squash and place, cut side down, on a rimmed baking tray covered with tinfoil. Bake for 30-40 minutes, until tender. Set aside to allow to cool enough to handle.
Lower oven heat to 350F.
In a medium skillet, melt the butter and cook the garlic until fragrant, about 2-3 minutes. Add the spinach and cook, stirring frequently, until it has wilted.
Add the cream, ricotta, and parmesan cheese to the skillet. Season to taste.
Keep at low heat until the cheese is melted and incorporated all together. Remove from heat.
Use a fork to fluff the strands of spaghetti squash from the shell. Pour half the spinach sauce over each squash half and stir into the squash.
Top each squash half with 1/2 cup of mozzarella cheese.
Bake at 350F for 15 minutes, then set oven to broil for an additional 3-5 minutes, until the cheese is golden on top.
