Cook pasta in lightly salted water and drain, reserving cup of cooking water. Transfer pasta to a large bowl and cover. Meanwhile, heat oil in a large nonstick skillet over medium-high heat, then add cauliflower and tsp salt. Cook 8 min and add tomatoes; continue cooking, turning occasionally, until cauliflower is golden and tomatoes break apart, 3 to 4 min more. Transfer to bowl with pasta and cover.

In a food processor, chop garlic and sage. Add prosciutto and pulse to chop coarsely. (If you don't have a food processor, chop sage and prosciutto with a knife.) Transfer mixture to skillet and cook, about 3 min. Add to pasta, along with arugula and Parmesan, and toss. Add a bit of reserved pasta water to moisten. Makes 4 to 6 servings.