Preheat oven to 425F or 400F convection. Line a baking sheet with parchment and add mushrooms, oil, thyme, and ½ teaspoon salt and immediately toss to coat. Spread out into an even layer and bake for 25 minutes or until cooked through and golden brown in spots, stirring halfway through.
Bring a large pot of salted water to a boil. Add pasta and cook to your desired doneness. Reserve 1 cup of pasta water, then drain and set aside.
In a high-speed blender, add the ricotta, parmesan, lemon, garlic, pepper, remaining ½ teaspoon salt, and ½ cup of the reserved pasta water. Blend until smooth and creamy.
Add pasta back to the pot along with the ricotta sauce and mushrooms and toss to coat. The pasta will continue to absorb the sauce as it sits, so keep your extra pasta water nearby (or use hot water) to add if it starts looking dry or you want it more saucy.
Serve right away topped with parsley (if using), plenty of parmesan, a drizzle of good olive oil, and black pepper.