Bring about 1 gallon of water to a boil in a medium pot. Add 1/4 cup salt to the water. Add the penne and cook until al dente, 12 to 15 minutes.
Drain the pasta and return it to the pot. While the pasta is still warm, add the arugula, hazelnuts, pecorino, oil, scallions and lemon juice. Toss to combine and to allow the arugula to wilt slightly. Serve sprinkled with pecorino,
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