Cook tortellini according to package directions. Meanwhile, in a large skillet, saute onion in oil until tender. Add garlic; cook 1 minute longer. Add the tomatoes, spinach, basil, salt and pepper. Cook and stir over medium heat until liquid is absorbed, about 3 minutes., Stir in cream and cheese. Bring to a boil. Reduce heat; simmer, uncovered, until thickened, 8-10 minutes. , Drain tortellini; toss with sauce. Sprinkle with additional cheese if desired.