My favorite part of a Hawaiian plate lunch is the scoop of Hawaiian macaroni salad. It's cold, tangy, and sweet, which is very appetizing when served with some kalua pork, ribs, or other tasty meats.
Fill a large 6-8 quart stock pot with water slightly more than halfway with water and bring to a boil. Add the macaroni, salt the water as desired, and cook on medium heat until soft (double the package cook time plus an extra minute, approximately 13 minutes total).
While the pasta cooks, use a fine grater to grate the carrots and onion into a bowl. You will only need about 1/2 cup of each and set aside whatever you can't safely grate (~2 pieces of carrot and 1/2 an onion) for other recipes.
Drain the macaroni in a colander and drain well. Transfer the macaroni to a large non-reactive mixing or serving bowl, add the apple cider vinegar, and stir. Allow the pasta to absorb some of the apple cider vinegar.
Add the chopped scallions, grated onion, and grated carrots to the macaroni.
In a small mixing bowl, combine the mayonnaise, milk, sugar, salt, and pepper and pour the mixture over the macaroni. Gently mix the ingredients together.
If stored overnight and/or the macaroni salad looks dry, add 1-2 heaping tablespoons of mayonnaise (as needed) to the macaroni salad and stir (optional).