Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 9x13-inch baking dish.

Bring a large saucepan of salted water to a boil. Add potatoes and cook until tender but still firm, about 15 minutes. Drain and mash.

While potatoes are cooking, combine ground beef and onion in a large skillet over medium-high heat. Cook and stir until beef is evenly browned and crumbly and onion is tender, 7 to 10 minutes. Drain.

Stir carrots, green beans, and condensed soups into beef mixture. Transfer to the prepared baking dish. Spread mashed potatoes over beef mixture and sprinkle Cheddar cheese over top.

Bake in the preheated oven until potatoes are lightly golden brown on top, about 30 minutes.