Preheat the oven to 350 degrees Fahrenheit.
Heat olive oil in a skillet over medium heat and add chopped onion. Cook until softened, about 3 minutes.
Add ground beef to the skillet and season with salt and pepper. Cook until the beef is browned, about 5 minutes.
Drain off any excess fat from the beef mixture and then add the can of tomato sauce and chili powder. Stir to combine all ingredients in the skillet.
Bring a pot of salted water to a boil and add the macaroni. Cook for 8-10 minutes or until al dente, stirring often.
Drain the macaroni and stir it into the beef mixture in the skillet.
Pour the mixture into a baking pan and cover with aluminum foil. Bake for 25 minutes, or until the sauce is bubbling.
Serve with grated cheese and a sprinkle of fresh parsley if desired.