Heat oven to 350°F. Grease 8-inch square (2-quart) baking dish. In large nonstick skillet, cook sausage over medium-high heat until browned, stirring occasionally. Drain.
In medium bowl, combine potatoes and Cheddar cheese. In greased baking dish, layer half of the potato mixture, all of the sausage mixture, spinach and tomatoes, remaining potato mixture, and all of the mozzarella cheese.
In medium bowl, beat eggs slightly. Add milk, salt and pepper; beat well. Pour evenly over potato mixture. Cover with foil.
Bake at 350°F. for 1 hour. Uncover; sprinkle with Parmesan cheese. Bake uncovered for an additional 15 minutes or until knife inserted in center comes out clean. Let stand about 5 minutes before serving; cut into squares.