2. In a medium skillet, heat 2 tablespoons of the olive oil over medium-low heat. Add the onion with a dash of salt and pepper and cook, stirring occasionally, until softened, about 4 to 5 minutes. Add the peas and cook for 3 minutes or longer, depending on their size and freshness. Add the mushrooms and cook for 5 minutes more.
3. Meanwhile, cook the pasta until it is al dente, about 10 to 12 minutes. Drain. Toss with the remaining olive oil, onion, peas, mushrooms, 2 tablespoons of the Parmesan cheese and 2 tablespoons of the parsley.
4. Divide the pasta among 4 warmed pasta bowls and sprinkle with the remaining Parmesan and parsley. Serve immediately.