Cook the macaroni according to package instructions. Drain and rinse with cold water
In a large bowl, combine the cooked macaroni, tuna, celery, tomatoes, relish, onion, and seasoning salt
In a separate small bowl, whisk together the mayonnaise, Dijon mustard, lemon juice, salt, and pepper
Pour the dressing over the macaroni mixture and toss until everything is well coated. Taste and adjust seasoning as necessary. If too dry, add more mayo or mustard
Refrigerate for at least 30 minutes to allow the flavors to come together
Serve chilled and enjoy your delicious Tuna Macaroni Salad!