Preheat oven to 425 degrees. Heat a large (5-quart) heavy pot or Dutch oven over high. Cook beef, breaking up meat with a spoon, until no longer pink, 4 to 5 minutes. Add onion and garlic; cook until softened, about 4 minutes

Add thyme and flour,stir until combined. Add 1/2 cup water and vegetables. Cook until vegetables are warmed through and liquid has thickened, about 3 minutes. Season with salt and pepper.

Spoon beef mixture into a 2-quart baking dish. Spread potatoes evenly over beef; using a fork, decorate potatoes add grated cheese and bake until potatoes are lightly browned, 10 to 15 minutes. Serve.