Spread hummus on a large plate with the back of a spoon, creating swirls and cavities. Drizzle it lightly with olive oil, just to freshen it up. Mix tomatoes, cucumbers, onion, lemon, about 1 1/2 tablespoons olive oil, plus salt and pepper to taste in a bowl. If you have sumac, add about 1/4 teaspoon. Stir in herbs. Heap salad on hummus, arrange pita wedges all around. Finish with additional za’atar, sumac, and/or fresh herbs.