Wash the peppers and chop them into small cubes. In a large skillet, heat the oil and add the onion. When golden, add the peppers and cook until they begin to turn golden. Add salt and pepper to taste.
Meanwhile, bring a large pot of salted water to a boil. Add the pasta. Cook the pasta until al dente. Drain the pasta, retain 1 cup of the cooking water. Add the pasta to the skillet with the peppers and cook together for about a minute. Add some of the retained water if it seems dry.
Serve immediately with a generous sprinkle Parmigiano Reggiano.