1. In large saucepot, cook pasta in boiling salted water 5 minutes; add frozen spinach and cook 10 minutes longer or until spinach is tender and pasta is al dente. Drain well, reserving 1/2 cup pasta cooking water.
2. Return pasta, spinach, and reserved cooking water to saucepot. Add ricotta, Parmesan, dried tomatoes, and 3/4 teaspoon salt. Heat over medium-low heat, tossing until pasta is evenly coated and heated through.