1. Cook the fettuccine according to package directions, omiting the salt if desired; drain, reserving 1 cup of the cooking water.
2. Return the pasta to the pot with 1/2 cup of the cooking water and place over low heat. Add the cheese, arugula, tomatoes, and pepper; toss until the cheese melts and the arugula just begins to wilt, about 1 minute. Add more of the cooking water if the pasta is too dry.