Preheat the oven to 350°F (175°C).
In a large skillet, cook the ground beef over medium-high heat until browned. Drain excess fat.
Add the diced onion and minced garlic to the skillet, cooking until the onion is translucent, about 3-4 minutes.
In a mixing bowl, combine the cooked elbow macaroni, diced tomatoes, cream of mushroom soup, sour cream, oregano, salt, and black pepper. Mix well.
Add the beef mixture to the bowl and stir until all ingredients are evenly combined.
Pour the mixture into a greased casserole dish and spread it out evenly.
Sprinkle the shredded cheddar cheese evenly over the top.
If desired, add crushed potato chips over the cheese for added crunch.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Remove from oven and let it cool for a few minutes before serving.