Arrange watercress, mixed salad and lettuce leaves on a large, flat platter with sliced red onion scattered throughout.
Cut haloumi into 3mm-thick slices. Heat a large, non-stick pan to medium-high heat, drizzle with the oil and fry haloumi for about 2 minutes on each side or until golden. Allow to cool.
Remove the shallow core and leaves of the persimmons. Slice in half down the middle, then cut into thick wedges. Arrange on the salad leaves with the cooled haloumi.
To make the dressing, whisk together buttermilk, sour cream, mustard, garlic and honey. Season with salt and pepper. Whisk in the olive oil, herbs and lemon juice. Add more seasoning to taste then pour over the salad and serve.