Bring a large pot of water to a boil, add 1 tablespoon of salt and the pasta, and cook according to the directions on the package, about 12 minutes, stirring occasionally. Drain the pasta in a colander and place it back into the pot. Immediately add the cream mixture and cook it over medium-low heat for 3 minutes, until most of the sauce has been absorbed in the pasta. Pour the hot pasta into a large bowl, add the arugula, Parmesan, tomatoes, and cooked broccoli. Cut the last lemon in half lengthwise, slice it 1/4-inch thick crosswise, and add it to the pasta. Toss well, season to taste, and serve hot.