If necessary, start by making your own gravy and set aside.
Preheat oven to 350 degrees F. Spray a 1 quart casserole dish with nonstick cooking spray and set aside.
In a medium saucepan over medium heat, melt 1 tablespoon butter or olive oil. Add onions and cook until translucent, stirring often; 4-5 minutes. Stir in frozen vegetables, minced garlic, salt, pepper and thyme. Cook for 1-2 minutes.
Add the turkey and gravy and stir until coated, then cook until heated through. Transfer to the prepared casserole dish and press into an even layer.
Heat mashed potatoes to lukewarm and spreadable. Stir in half of the shredded cheese, then spread the potatoes over the turkey mixture in the casserole dish. Top with remaining shredded cheese.
Bake in the 350 degree oven for 30 minutes, or until top is golden and sides are bubbly. For a more browned top, flip on the broiler during the last 5 minutes.
Garnish with fresh minced parsley and serve warm.