Whisk together the blueberry vinegar, sugar, ground coriander, salt and black pepper and bring to a boil.
Place fresh blueberries in a heatproof container (I used a canning jar) and pour brine over them. Cover and refrigerate 6-8 hours or overnight.
Drain blueberries, reserving pickling vinegar.
Slice Halloumi cheese into strips and heat over low heat in a nonstick skillet until golden, turning to brown all sides.
Divide lettuces among salad plates, layering cheese pieces on top along with drained blueberries, shaved red onion slivers, and pistachio nuts.
Whisk extra virgin olive oil into the pickling vinegar until emulsified, seasoning with additional salt and pepper to taste (if desired). Serve dressing over salad.