Cook the macaroni according to the package directions. Drain and run under cold water to cool.
Meanwhile, place the eggs in a small saucepan and add enough cold water to cover them by 1 inch. Bring to a boil. Remove from heat, cover, and let stand for 12 minutes. Drain and run under cold water to cool. Peel the eggs and coarsely chop.
In a large bowl, whisk together the mayonnaise, lemon juice, ½ teaspoon salt, and ¼ teaspoon pepper. Add the macaroni, chopped eggs, scallions, celery, and parsley and toss gently to combine.