1.Preheat oven to 240°C fanbake. Cook baby potatoes in boiling water until al dente (8-10 minutes). Drain, cool slightly and cut into quarters.
2.Heat oil in a large ovenproof frying pan over medium-high heat. Season lamb racks and sear, turning occasionally, until golden (about 8 minutes). Set aside.
3.Add potatoes to pan. Combine beans, garlic and shallots and add to potatoes. Season to taste, toss to combine, place lamb on top and roast in oven until lamb is medium-rare (10-15 minutes).
4.Remove lamb and rest for 5 minutes. Scatter mint and oregano over bean mixture, toss, season to taste and squeeze over lemon juice. Serve with lamb and lemon wedges.