Prepare tortellini according to package directions; drain and set aside.
Meanwhile, in a bowl, combine marinara sauce, mascarpone or cream cheese, parsley and thyme. Fold in tortellini. Transfer to a greased 9"x9" baking pan. Top with mozzarella and Parmesan cheeses.
Bake, covered, at 350 degrees for about 30 minutes, or until cheese is melted and sauce is bubbly.