Preheat oven to 350 degrees F (175 degrees C) and lightly grease a 2 quart baking dish.
In a large skillet over medium-high heat, stir and cook ground beef, onion and celery until juices run clear. Drain. Pour mixture into baking dish with vegetable soup and thyme; stir well. Spread mashed potatoes on top.
Bake 20 minutes. Sprinkle shredded cheese on top and bake 5 minutes more, or until cheese has melted.