Place the noisettes into a large shallow dish. Mix together 3 tbsp olive oil, rosemary, cider vinegar, and lemon zest and juice. Season and pour over the noisettes. Cover and refrigerate for 2-3 hours.
Preheat the oven to 200&176;C, 400&176;F, Gas Mark 6.
Heat the remaining oil in a large pan, remove the lamb from the marinade (reserve for later) and sear for 2-3 minutes, turning once until brown on both sides.
Transfer to a hot roasting tin, add a little of the marinade mixture and cook for a further 8-10 minutes according to how pink you like your lamb.
Place the salad ingredients into a large salad bowl. Place the dressing ingredients into a screw-topped jar, season and shake until combined. Pour over the salad.
Arrange the noisettes onto a plate, garnish with extra rosemary and spoon over the jus from the roasting tin. Serve with saut&233; potatoes and the watercress and pink grapefruit salad.