Boil macaroni for about 15 minutes or until done (don't let it cook too much). Mix milk, onion, garlic, Maggi, green pepper, and mayo in a bowl.
Take a baking pan and grease it with butter. Take the boiled macaroni and stir it with the mix ingredients. Pour a little bit of the macaroni in the pan then spread cheddar cheese over it. Then put more macaroni on top of it and add more cheese.
Preheat oven to 350 degrees F. Bake it for about 45 minutes or until top is brown.