Drain the tuna and chickpeas thoroughly using a fine-mesh sieve.
In a medium mixing bowl, flake the tuna into bite-sized pieces using a fork.
Add the chickpeas, cucumber, red onion, and olives to the tuna.
In a small whisking bowl, combine olive oil, lemon juice, oregano, salt, and pepper until emulsified.
Drizzle the dressing over the salad and toss gently to coat.
Fold in the fresh parsley just before serving.