Preheat oven to 180°C (350°F).
In a large pan, cook the ground beef over medium heat until browned.
Add the onion and garlic, and sauté until the onion is translucent.
Stir in the diced tomatoes, tomato paste, and oregano. Cook for about 10 minutes, allowing the sauce to thicken. Season with salt and pepper.
Meanwhile, cook the pasta according to package instructions, drain, and set aside.
In a large casserole dish, combine the cooked pasta, beef mixture, and half of the shredded cheddar cheese. Mix well.
Top the casserole with the remaining cheddar cheese.
Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.