Preheat the grill to high. Warm the pita breads under the grill for a few seconds or until puffy, then carefully split them open through the middle and open out each one like a book. Return to the grill and toast for 2–3 minutes on each side or until lightly browned and crisp. Roughly tear the pita into bite-sized pieces and set aside until needed.
Whisk together the olive oil and lemon juice in a large serving bowl, and season with salt and pepper to taste. Add the spring onions, tomatoes, cucumber and tuna, then toss gently to coat with the oil and lemon juice.
Add the parsley, coriander, mint and torn pita pieces to the serving bowl and toss quickly to mix. Serve immediately.