For the marinade, mix the lemon halves, lemon juice and olive oil in a bowl. Add the rosemary and season to taste. Coat the lamb steaks in the marinade and leave in the bowl for 20 to 30 minutes.
Heat a griddle pan and cook the lamb for about 3 minutes on both sides.
While cooking, slice the beetroot and arrange around the edge of a serving plate. Add the rocket leaves and beans and decorate with the orange segments.
For the dressing, mix the olive oil with the remaining orange juice in a jug. Spoon in the mustard and sugar and stir well.
Place the lamb in the centre of the plate, drizzle with the dressing and top with chives.