Preheat and prep the squash. Heat the oven to 400°F (200°C). Slice the spaghetti squash in half lengthwise. Scoop out seeds. Drizzle the cut sides with 1 tablespoon olive oil and season with salt and pepper.

Roast. Place squash cut-side down on a parchment-lined baking sheet. Roast 35–45 minutes, until the flesh is tender and strands pull away easily with a fork. Set aside to cool slightly.

Cook the sausage. While the squash roasts, heat 1 tablespoon olive oil in a large skillet over medium heat. Add Italian sausage, breaking it up with a spatula. Cook until browned and cooked through, about 6–8 minutes. Drain excess fat if needed, leaving about 1 tablespoon in the pan.

Sauté the garlic. Push sausage to the side of the skillet. Add butter and garlic to the open space and cook 30–60 seconds until fragrant, stirring to prevent burning.

Build the Alfredo base. Reduce heat to medium-low. Stir in heavy cream and chicken broth, scraping up any browned bits from the pan. Add cream cheese and whisk until melted and smooth.

Cheese and season. Add Parmesan, Italian seasoning, crushed red pepper flakes, and a pinch of black pepper. Simmer gently 2–3 minutes until thick and glossy. Taste and adjust salt and pepper as needed.

Add optional veggies. If using spinach or other add-ins, fold them into the sauce now and cook just until tender.

Shred the squash. Use a fork to scrape the squash flesh into spaghetti-like strands. Pat with paper towels if very watery.

Combine. Add squash strands to the skillet and toss gently with the sausage Alfredo until well coated. If the sauce is too thick, splash in a little more broth or cream. If too thin, let it simmer a minute to tighten up.

Finish and serve. Sprinkle with extra Parmesan and chopped parsley. Serve hot.