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

Roast: Place squash halves cut-side down on a baking sheet lined with parchment. Roast for 35–45 minutes, until the flesh is tender and strands pull away easily with a fork. If the squash is smaller, start checking at 30 minutes.

Make the meat sauce: While the squash roasts, heat the remaining 1 tablespoon olive oil in a large skillet over medium-high heat. Add the ground beef, season with salt and pepper, and cook, breaking it up, until browned and no longer pink, 5–7 minutes. Drain excess fat if needed.

Build flavor: Add onion to the skillet and cook until softened, about 3–4 minutes. Stir in garlic and tomato paste; cook 30–60 seconds until fragrant and slightly darkened.

Simmer the sauce: Pour in crushed tomatoes or marinara. Add oregano, dried basil, and red pepper flakes if using. Lower the heat and simmer 10–15 minutes, stirring occasionally. Taste and adjust salt and pepper. The sauce should be thick and savory.

Shred the squash: When the squash is done, flip the halves over. Let cool a couple of minutes, then use a fork to pull the flesh into spaghetti-like strands, keeping them in the shells. Leave a thin border so the “boats” stay sturdy.

Add cheese and sauce: Sprinkle Parmesan over the warm squash strands and toss gently to coat. Spoon a generous amount of meat sauce into each half. Top with mozzarella.

Broil to finish: Set your oven to broil. Return the stuffed halves to the oven for 2–4 minutes, until the cheese is melted and lightly golden. Watch closely to prevent burning.

Garnish and serve: Let rest a couple of minutes. Finish with chopped fresh basil or parsley and extra Parmesan. Serve hot, right in the squash boats or scooped onto plates.