For the dressing, place the olive oil, lemon juice and zest, crushed garlic and sumac into a bowl and whisk together to combine. Season, to taste, with salt and freshly ground black pepper. (You will not need all the dressing for this recipe, so set the remainder aside in the fridge for up to a week.)
For the salad, place the torn pitta, tomatoes, cucumber, pepper, radishes, shallot, rocket leaves, Little Gem lettuce leaves and mint leaves into a large bowl and season, to taste, with salt and freshly ground black pepper.
To serve, pour the dressing, to taste, over the salad and gently mix together to coat the salad evenly.