Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, brown the ground beef, breaking it apart with a spoon, until fully cooked. Drain any excess fat.
Add the diced onion and bell pepper to the skillet with the ground beef and cook until softened, about 5 minutes.
Stir in the mixed vegetables, garlic powder, onion powder, salt, and pepper. Mix until well combined.
In a mixing bowl, combine the cream of mushroom soup with the milk. Stir until smooth.
In a greased 9x13-inch baking dish, layer half of the sliced potatoes at the bottom. Spread the beef and vegetable mixture evenly over the potatoes. Pour the soup mixture on top.
Layer the remaining sliced potatoes over the beef mixture. Top with shredded cheese.
Cover the baking dish with aluminum foil, making sure it doesn't touch the cheese.
Bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15 minutes, or until the potatoes are tender and the cheese is bubbly and golden.
Let the casserole cool for a few minutes before serving.