Whisk all the ingredients together vigorously in a small bowl (or shake well in a jar). Set aside for later.
Prepare the salad:
Wash all vegetables and drain well.
Cut romaine into strips or bite-sized pieces.
Cut the cucumber into thin slices.
Chop red onions, cut in half and thinly slice.
Also cut the radishes into thin slices.
Pluck the mint from the stems and roughly chop.
Halve the cherry tomatoes and quarter the large ones.
For the pita chips, cut the pita bread into bite-sized pieces. Mix it with a few dashes of olive oil, salt and pepper. Then bake in the oven at 200 °C for about 10 minutes until golden and crispy.
In a large bowl, combine the romaine, cucumber, red onion, tomatoes, radishes, mint and half the pita chips. Drizzle with the lemon dressing.
Serve the salad topped with the remaining pita chips, plus a sprinkling of sumac and freshly ground black pepper.