Southern Tuna Macaroni Salad

Place diced onion in a large bowl and cover with cold water. Let sit for 5 minutes. Drain into a colander. While onion soaks, bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes. Drain into the same colander as red onion and run under cold water to stop cooking and cool to room temperature. Place mayonnaise, pimentos, relish, chow-chow, mustard, Cajun seasoning, and salt in a large bowl and stir to combine. Add pasta, red onion, and celery and stir to combine. Gently fold in tuna and eggs to combine.