Set the oven at 400° F (200° C). Place the bread squares on a baking sheet and toast them in the oven for 8 minutes or until lightly browned; set aside.
In a bowl, toss the cucumbers, tomatoes, radishes, scallions, mint, and parsley.
In another bowl , whisk the lemon juice, salt, pepper, olive oil, and sumac until blended. (Sumac is an essential spice made from the dried, powdered berries of the sumac tree.)
On a large platter with a raised rim, arrange the lettuce leaves.
Spoon the cucumber mixture over the leaves. Scatter the bread pieces on top.
Sprinkle with dressing and more salt and pepper.
Note: recipe from The Lebanese Cookbook by Hussien Dekmak.