Mix the minced beef together with egg, water and the bread crumbles. Divide it in 4.
Press the meat in to hamburger shapes and let it rest 30 minutes in the fridge.
Cut the haloumi cheese in slices.
Put the hamburgers on the grill, and in the meanwhile cut the onion in thin slices.
Place the hamburger breads on plates and place the salad leaves, onion slices and the cheese slices on the bottom part of the bread.
Put the haloumi slices on the grill.
Place the hamburgers on the cheese slices, and then place the haloumi cheese on the haloumi. Sprinkle it all with some arugula.
Serve a light summer salad on the side.