Cook pasta according to package directions until al dente, about 8 minutes. Drain and rinse under cold water; set aside.

In a large mixing bowl, add tuna, peas, diced onion, celery, and pickles; set aside.

In a small bowl, whisk together mayonnaise, milk, sugar, seasoning salt, and freshly ground black pepper.

Add pasta to the mixing bowl with tuna and veggies. Pour ¾ of the dressing over salad, stir until well combined and evenly coated (refrigerate leftover dressing).

Cover the salad and refrigerate for at least 1 hour before serving. Just before serving add more dressing if desired.

Pour salad into a serving bowl. Garnish with chopped celery leaves and more freshly ground black pepper.