Step 1: Roast the Spaghetti Squash : Preheat oven to 400°F (200°C). Slice spaghetti squash in half lengthwise and scoop out the seeds. Brush each half lightly with olive oil and season with salt and pepper. Place cut-side down on a baking sheet lined with parchment paper. Roast for 30–40 minutes until tender. Once cool enough to handle, use a fork to scrape out the “spaghetti” strands into a large bowl. Set aside.

Step 2: Prepare the Ground Beef Sauce : Heat olive oil in a large skillet over medium heat. Add the ground beef and cook, breaking it up with a spoon, until browned (about 6–8 minutes). Drain excess fat if needed. Add chopped onion and minced garlic. Sauté for 2–3 minutes until fragrant and translucent. Stir in tomato sauce, diced tomatoes, tomato paste, basil, oregano, red pepper flakes, salt, and pepper. Simmer on low heat for 10 minutes to let the flavors combine.

Step 3: Combine the Squash and Sauce : Add the shredded spaghetti squash to the skillet with the sauce. Stir until everything is evenly coated in the rich tomato-beef mixture.

Step 4: Assemble the Casserole : Lightly grease a 9x13-inch baking dish. Spread half of the squash mixture into the dish. Dollop spoonfuls of ricotta (or cottage cheese) evenly over the top. Add the remaining squash mixture and top with mozzarella and Parmesan cheese.

Step 5: Bake : Reduce oven temperature to 375°F (190°C). Bake uncovered for 20–25 minutes, until the cheese is melted, golden, and bubbly.

Step 6: Serve : Remove from oven and let rest for 5 minutes. Garnish with fresh basil or parsley before serving. Slice into squares and serve warm.