In a large skillet over med-high heat, brown the ground beef until completely cooked and no longer pink. Transfer to a bowl using a slotted spoon and drain off all but 2 tablespoons of fat.
Add the onion to the pan and sauté until softened. Add the garlic and cook for 1 minute. Stir in the salt, pepper and garlic powder. Return the beef to the pan. Stir in the milk, chicken stock and macaroni. Bring the mixture to a boil and then turn to heat to low.
Cover and simmer for 10 minutes or until the macaroni is tender.
Remove from the heat and stir in the cheese until melted. Serve immediately.