Preheat your oven to 375 degrees Fahrenheit. Lightly grease a 9x13 inch baking dish.
Cook the beef. In a large skillet over medium heat, brown the ground beef with the diced onion until the beef is no longer pink. Drain any excess fat.
Add the garlic. Stir in the minced garlic and cook for one more minute until fragrant.
Make the sauce. Reduce the heat to low.
Stir in the cream of mushroom soup, sour cream, milk, salt, pepper, and oregano. Mix until everything is well combined and smooth.
Layer the dish. Spread the beef mixture evenly into the prepared baking dish. Sprinkle 1 cup of the mozzarella cheese on top.
Add the bread. Arrange the cubed garlic bread over the cheese layer in a single, even layer.
Press them down slightly into the sauce.
Top with cheese. Sprinkle the remaining 1 cup of mozzarella cheese over the bread cubes.
Bake. Place the dish in the preheated oven and bake for 20 to 25 minutes, or until the cheese is melted and bubbly and the bread is golden brown.
Rest and serve. Let the casserole sit for 5 minutes before serving. Garnish with fresh parsley if you like.