Bring a small saucepan of water to the boil and add the eggs, taking care not to break the shells. Simmer gently for 6 minutes. Remove and cool under cold running water.
Meanwhile, heat a ridged griddle pan and toast the pitta breads for 2–3 minutes, turning once, until toasted and nicely charred.
Rub 1 tablespoon of the olive oil over the tuna steaks, then season with salt and pepper. Place on a baking sheet and slide under a preheated grill for 3–4 minutes until almost cooked, turning once. Set aside to cool.
Cut up the toasted pitta bread and place in a large bowl with all the chopped vegetables and herbs. Mix together the harissa, lemon juice and remaining olive oil and stir into the salad, to coat. Season generously with salt and pepper.
Divide the salad on to serving plates. Cut the eggs into wedges and arrange over the salads. Top each salad with a tuna steak and serve sprinkled with the crushed sumac.