Preheat the oven to 350 degrees. Spray a 9x13 inch baking dish with cooking spray. In a large pot of boiling water, cook the pasta according to the package directions. Drain Well.
In a large skillet, heat the oil over medium-low heat. Add the onions and cook until soft, about 5 minutes. Stir in the garlic and cook for 30 seconds. Stir in the beef and cook until browned; season with salt and pepper. Stir in the tomato paste, then add the diced tomatoes and mustard. Let the mixture bubble until it is slightly thickened, about 2 minutes. Season with your salt and pepper.
Put your noodles in the greased pan and pour your meat sauce on top. Slightly mix together your noodles and sauce. Cover with foil and cook for 20 minutes. Take it out of the oven and remove your foil. Add your cheese on top and stick back in the oven until the cheese is melted. (5 to 10 minutes). Serve while it is warm.