1Prepare spaghetti according to al dente directions. Drain and set aside.
Preheat oven to 350.
2Sauté mushrooms in oil, add peppers and onions. Cook until starting to soften, add garlic and sausage. Continue to stir and cook. Add spinach and stir to wilt the spinach. Lightly salt and pepper as you sauté.
3Pour sauce into casserole dish, add pasta and toss. Add sautéed ingredients and toss to evenly coat everything. Top with Parmesan. Bake, uncovered, 20-30 minutes until cheese is melted and golden.