Cook potatoes and arugula in a large quantity of boiling salted water for 5 minutes. Add pasta and continue to cook for 8 minutes. Meanwhile, put the oil, garlic, and red pepper flakes in small saucepan and cook over low heat until the garlic turns light golden brown about 1 minute. Remove from heat. Add to the drained potatoes, arugula and pasta. Toss with cheese and serve.