Bring a large pot of water to a boil. Add pasta; cook until tender, 8 - 10 minutes or according to package directions. Drain and transfer to a large bowl.
Meanwhile, heat oil in a large nonstick skillet over medium heat. Add onion and garlic and cook, stirring, until soft and beginning to brown, about 3 minutes. Add mushrooms, salt and pepper and cook, stirring, until the mushrooms release their liquid, 4-6 minutes.
Add tomatoes, spinach and crushed red pepper. Increase heat to medium-high; cook, stirring once halfway through, until the spinach is wilted, about 4 minutes.
Toss the sauce and tofun with the pasta and divide among 4 bowls. Top off with 1/4 cup of ricotta cheese to each bowl.