First, preheat oven to 350 degrees Fahrenheit.
Cut squash in half. Remove seeds. Roast cut side down for 30 to 40 minutes, until the skin is soft enough to push down. Gently scrape a fork across the flesh to pull back and separate the strands of squash. For better baking and presentation, leave the strands in the shell. You can prepare the sauce layers while the squash is roasting.
To make the sauce layer, sauté mushrooms, bell pepper, and sweet onion.
Once sautéed, add to marinara. Set aside.
Mix egg, Parmesan cheese, garlic, and basil/parsley into the ricotta.
Layer the marinara mixture and ricotta mixture on top of the squash halves, evenly distributed.
Top with mozzarella. Bake for 20 minutes, or until warm, bubbly, and browned on top. Serve hot with your favorite salad!