Thaw and drain spinach. Press out excess liquid. In a large skillet melt butter. Add mushrooms and cook about 5 minutes or until tender, stirring often. Add the undrained tomatoes, tomato sauce, wine, pepper and fennel. Bring to boiling; reduce heat and cover. Simmer over low for 5 minutes.
Meanwhile, cook ravioli according to package directions. Gently toss ravioli with tomato mixture and spinach. Transfer to an ungreased 1.5 qt. casserole. Top with cheese. Bake, uncovered in a 350 oven for 20 minutes or until heated through. Makes 4 main dish servings.
Make ahead: Follow above directions for assembly of casserole. Cover and refrigerate, unbaked, for up to 24 hours. Bake at 180ºC or 40 minutes or until heated through.