Prep the base: Drain the tuna thoroughly.
Rinse the chickpeas and pat them dry. Add both to a large mixing bowl and flake the tuna with a fork.
Chop the crunch: Add red onion, celery, cucumber, and red bell pepper. Sprinkle in the parsley and lemon zest.
Make the dressing: In a small bowl, whisk lemon juice, olive oil, Dijon, cumin, and crushed red pepper.
Season with salt and black pepper.
Toss to combine: Pour the dressing over the salad and gently fold until everything is coated. Taste and adjust lemon, salt, and pepper.
Add extras if using: Fold in feta, avocado, capers, or olives. If using avocado, add just before serving.
Rest and serve: Let the salad sit for 10 minutes so flavors meld.
Serve over greens, stuffed in a pita, or alongside cooked grains.