Heat oven to 375°F. Lightly spray medium skillet with cooking spray. Cook mushrooms and onion in skillet over medium-low heat 4 minutes or until onion is tender; remove from heat. Add spinach, 1/4 cup mozzarella cheese and Parmesan cheese; mix well. Set aside. In large bowl, combine turkey, oats, milk, egg white, Italian seasoning, salt and pepper; mixing lightly but thoroughly. Spoon 2/3 of turkey mixture lengthwise down center of 11 x 7-inch glass baking dish. Form a deep indentation down middle of turkey; fill indentation with reserved spinach mixture. Top with remaining turkey, forming a loaf. Seal edges to completely enclose spinach filling. Bake 30 to 35 minutes or until thermometer registers 170°F and juices show no pink color. Remove from oven; sprinkle with remaining mozzarella cheese. Return to oven 1 to 2 minutes or until cheese melts. Let stand 5 minutes before slicing.