Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook according to package directions until al dente, usually about 8-10 minutes. You want the pasta to have a slight bite because it will soften a bit as it sits in the dressing.

Drain well and rinse under cold water to stop the cooking process and cool it down quickly. This step matters because warm pasta can make your mayonnaise separate and turn the salad greasy.

In a large mixing bowl, whisk together the mayonnaise, lemon juice, Dijon mustard, garlic powder, and a pinch of salt and pepper.

Taste the dressing and adjust the seasoning as needed before the other ingredients go in.

Add the cooled macaroni to the bowl with the dressing. Toss gently until every piece is coated.

Fold in the drained tuna, breaking up any large chunks with your spoon.

Add the diced celery, red bell pepper, red onion, and sweet pickle relish and stir to combine.

If using hard-boiled eggs, fold them in gently so they don't turn to mush.

Cover the bowl with plastic wrap and refrigerate for at least one hour before serving to allow the flavors to marry and the pasta to soak up the dressing.

Give it a good stir before serving, and add a splash more mayo or lemon juice if it looks dry. The salad should be creamy and luscious, not stiff or clumpy.