01 - Preheat the oven to 400°F. Halve the spaghetti squash lengthwise, scoop out seeds, and place cut side down on a parchment-lined baking sheet. Roast for 40 minutes or until the flesh is tender.
02 - Allow squash to cool briefly, then use a fork to scrape out the flesh into spaghetti-like strands. Set aside and cover to keep warm.
03 - In a large skillet over medium-high heat, cook ground beef until browned, breaking up any clumps. Add diced onion and minced garlic; sauté until onion is translucent.
04 - Stir in diced tomatoes, tomato paste, Italian seasoning, salt, and pepper. Reduce heat to low and simmer uncovered for 20 minutes, stirring occasionally, until sauce thickens.
05 - Divide spaghetti squash strands among plates. Spoon hearty Bolognese sauce over the squash and garnish generously with freshly grated Parmesan cheese. Serve immediately.