Bring a large pot of salted water to a rolling boil.
Add the macaroni and stir; return to a boil, then reduce heat slightly and cook until al dente (about 15 minutes for Fiber Gourmet Light elbows).
Drain the pasta in a colander and let it sit to remove excess water.
While the pasta cooks, drain the canned tuna in a fine-mesh strainer set over a bowl to remove oil.
Chop 20 of the green olives and slice the remaining olives for garnish.
Finely chop the celery and slice the green onions.
Whisk together lemon juice (and zest if using) and some olive brine, then whisk in mayonnaise and any desired seasoning to make the dressing.
In a large bowl, combine the cooked macaroni, chopped olives, chopped celery, and sliced green onions.
Add the desired amount of dressing and toss until the ingredients are evenly coated; reserve any extra dressing for leftovers.
Gently fold in the drained tuna, keeping it in small chunks without overmixing.
Season to taste with salt and fresh-ground black pepper, keeping in mind the olives add saltiness.
Serve immediately or chill before serving.