Preheat and prep: Set your oven to 400°F (200°C). Line a baking sheet with parchment for easy cleanup. Carefully halve the spaghetti squash lengthwise and scoop out the seeds.

Roast the squash: Brush the cut sides with 1 tablespoon olive oil and season with salt and pepper. Place cut-side down and roast for 35–45 minutes, until the skin gives slightly when pressed and the strands pull apart easily with a fork.

Start the broccoli: While the squash roasts, heat 1 tablespoon olive oil in a large skillet over medium. Add the onion (if using) and cook 3–4 minutes until soft. Add the broccoli, 2 tablespoons water, and a pinch of salt. Cover and steam-sauté 3–5 minutes, until bright green and crisp-tender.

Add garlic and spices: Push the broccoli to the edges of the skillet. Add a drizzle of oil if the pan looks dry. Stir in the garlic, red pepper flakes, Italian seasoning, and smoked paprika. Cook 30–60 seconds, just until fragrant.

Brown the sausage: Slice the chicken sausage into coins. Add to the skillet and cook 3–4 minutes, stirring occasionally, until lightly browned and heated through. Taste and adjust salt and pepper.

Shred the squash: When the squash is tender, let it cool just enough to handle. Use a fork to pull the strands into “spaghetti.” Transfer to a colander and gently press with tongs to release excess moisture.

Bring it all together: Add the squash strands to the skillet with the broccoli and sausage. Add the butter (if using), Parmesan, lemon zest, and a squeeze of lemon juice. Toss over low heat for 1–2 minutes until everything is coated and steamy.

Finish and serve: Taste and adjust seasoning. Top with more Parmesan, a drizzle of olive oil, and chopped parsley or basil. Serve warm.