For the labne, combine yoghurt and salt together, mixing until well combined. Line a sieve with two pieces of clean chux and pour the yoghurt mixture into the centre. Bring the edges of the chux together and secure tightly with a rubber band, to enclose the yoghurt mixture. Place sieve over a bowl and refrigerate for 12 hours.
For the pickled cucumber, place vinegar, sugar, zest and oregano together in a mixing bowl, stirring until sugar dissolves. Add cucumber and onion, stirring to combine and refrigerate for 15 minutes.
To assemble salad, spread labne across the base of a large serving platter and sprinkle over 1 teaspoon sumac and freshly ground black pepper. In a large mixing bowl combine watermelon, beans, fennel, drained pickled cucumber and red onion, tossing gently to combine. Place mixture over the labne and sprinkle over the pomegranate seeds, mint, pistachios, remaining sumac, salt and pepper to taste.