Start by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add elbow macaroni and cook according to package instructions until al dente, about 7–8 minutes. Drain and rinse under cold water.

In a mixing bowl, whisk together mayonnaise, mustard, salt, and pepper until smooth and well combined.

Chop celery, bell peppers, onion, and hard-boiled eggs into small, bite-sized pieces.

In a large mixing bowl, combine the cooled macaroni and chopped vegetables, ensuring everything is well mixed.

Pour the prepared dressing over the pasta and vegetable mixture, gently folding to coat everything evenly.

Cover the salad and refrigerate for at least 30 minutes before serving to allow flavors to meld.