Preheat oven to 350 degrees. Lightly grease a 9x13 baking dish with non-stick spray. In a medium bowl, whisk together soup, milk, garlic powder, onion powder, rosemary, and thyme. Season with salt and pepper. Spread mashed potatoes in an even layer in baking dish, then top with shredded chicken. Pour sauce over chicken and top with cheese. Bake for 25-30 minutes, or until hot and bubbly. Let cool 5-10 minutes before serving.