Preheat your oven to 350°F (175°C).

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until the onion is translucent, about 3-4 minutes.

Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned and no longer pink, about 6-8 minutes. Drain excess fat if necessary.

In a large bowl, combine the cream of mushroom soup, milk, salt, black pepper, and paprika. Mix well.

In a greased 9x13-inch baking dish, layer half of the sliced potatoes on the bottom. Spread half of the cooked beef mixture over the potatoes, followed by half of the soup mixture. If using, sprinkle half of the frozen mixed vegetables on top.

Repeat the layers with the remaining potatoes, beef mixture, soup mixture, and vegetables.

Cover the baking dish with aluminum foil and bake in the preheated oven for 45 minutes.

Remove the foil, sprinkle the shredded cheddar cheese on top, and bake for an additional 15-20 minutes, or until the cheese is melted and bubbly, and the potatoes are tender.

Let the casserole cool for 5-10 minutes before serving.