In a large mixing bowl, combine ground beef, finely grated onion, minced garlic, egg, breadcrumbs, milk, salt, pepper, and dried oregano. Mix until just combined and form into small meatballs, then set aside.

Heat a skillet over medium heat and add olive oil. Once hot, brown the meatballs in batches for 5–7 minutes until golden.

Preheat oven to 375°F (190°C). Slice medium potatoes thinly and toss with olive oil, paprika, salt, and pepper.

Grease a baking dish with olive oil. Layer half of the potato slices, followed by meatballs, then half of the cheese. Repeat with remaining potatoes and cheese.

Cover with aluminum foil and bake for 30 minutes. Remove foil and bake for an additional 10 minutes until golden brown.

Let the casserole rest for 5 minutes before serving. Garnish with freshly chopped parsley.