Preheat oven to 425. Line a baking sheet with aluminum foil. Spread the tomatoes onto the sheet and drizzle with olive oil. Season liberally with salt and pepper. Roast your tomatoes for 10-12 minutes. Transfer the pan to a wire rack and set aside.
In a large skillet over medium heat melt 3 tablespoons butter. Add in the mushrooms and cook for 6-7 minutes, stirring occasionally. Add the garlic, crushed red pepper and season well with salt and pepper. Continue cooking for another 3 minutes.
While the mushrooms are cooking, bring a large pot of salted water to a boil. Cook the spaghetti according to package directions. Reserve 3/4 cup pasta water, and drain pasta.
Add the remaining 3 tablespoons butter to the mushrooms and melt. Add in the drained pasta, pasta water, and 3/4 cup Parmesan cheese. Mix thoroughly to coat pasta and melt cheese.
Sprinkle with parsley and fold in roasted tomatoes.
