For the Harissa Vinaigrette: Add all ingredients to a bowl then whisk to emulsify. Set aside.
To Assemble and Serve: In a bowl, dress watermelon and cucumbers with lime juice, Maldon salt, sumac, mint, and some Harissa Vinaigrette.
Spoon whipped labneh onto a serving plate then add the watermelon and cucumber salad.
Garnish with smoked feta and serve with fried pita.
