Preheat the oven to 350°F (175°C).
Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened, about 3-4 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and no longer pink, about 7-8 minutes.
Drain excess fat from the skillet if necessary.
Season the beef mixture with salt, black pepper, and dried oregano. Stir well to combine.
In a large mixing bowl, combine the softened cream cheese, sour cream, and milk. Mix until smooth and creamy.
Add the cooked ground beef mixture and cooked elbow macaroni to the cream cheese mixture. Stir until everything is evenly combined.
Transfer the mixture to a greased 9×13 inch casserole dish and spread evenly.
Sprinkle 1/2 cup of shredded cheddar cheese evenly over the top.
Bake in the preheated oven for 20 minutes, then remove and sprinkle the remaining 1/2 cup cheddar cheese on top.
Return to the oven and bake for an additional 5-10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let the casserole cool for 5 minutes before serving.