Heat oven to 450°F. Spray 13x9-inch (3-quart) baking dish with nonstick cooking spray.
Spray large nonstick skillet with nonstick cooking spray. Add turkey, onion, garlic powder and thyme; cook over medium-high heat until turkey is browned. Stir in milk, green beans, soup, water chestnuts and mushrooms. Bring to a boil. Pour turkey mixture into sprayed baking dish. Top with potato nuggets.
Bake at 450°F. for 20 to 25 minutes or until hot and bubbly. Let stand 5 minutes before serving.