Coat a nonstick skillet with cooking spray; place over medium-high heat until hot. Add mushrooms, and saute until tender. Remove from heat, and set aside.
Drain spinach, and press between paper towels to remove excess moisture. Set aside.
Combine cream cheese and next 3 ingredients in a bowl; beat at medium speed of an electric mixer until creamy. Stir in mushrooms and spinach. Spoon spinach mixture into 4 individual gratin dishes coated with cooking spray; set aside.
Coat skillet with cooking spray; place over medium-high heat until hot. Add scallops, and cook 3 minutes, turning scallops to lightly brown on all sides. Place scallops evenly over spinach mixture in gratin dishes; sprinkle with Parmesan cheese. Bake at 375° for 15 minutes or until thoroughly heated and lightly browned.