Preheat your oven to 400°F (200°C). Carefully slice the spaghetti squash lengthwise and scoop out the seeds. Brush the cut sides with olive oil and season with salt and pepper. Place cut-side down on a parchment-lined baking sheet.

Roast for 35–45 minutes, until the flesh is tender and easily pierced with a fork. Remove from the oven and let cool slightly. Use a fork to scrape the flesh into spaghetti-like strands. Set aside.

Heat olive oil or butter in a large skillet over medium heat. Add the chopped onion and cook for 3–4 minutes until softened. Add minced garlic and cook for another 30 seconds until fragrant.

Add ground beef to the skillet. Break it apart with a wooden spoon and cook until browned and fully cooked. Drain excess fat if necessary, but leave some for flavor.

Stir in tomato paste and cook for 1–2 minutes to deepen the flavor. Add crushed tomatoes, beef broth, Italian seasoning, oregano, basil, salt, black pepper, and red pepper flakes if using.

Reduce heat to low and let the sauce simmer uncovered for 20–30 minutes, stirring occasionally. The sauce should thicken and develop rich flavor.

You can either serve the bolognese over spaghetti squash or mix the squash directly into the sauce. Taste and adjust seasoning as needed.