Preheat oven to 180ºC / Gas Mark 5.
- Soak wooden skewers in water for 15 minutes.
- Liquidise the watercress, pine nuts, garlic and cheese in a blender and gradually pour in the oil.
- Heat a frying pan or skillet and brown the lamb cutlets on both sides. Remove from the pan and put into a roasting dish. Spread the pesto onto the lamb.
- Thread tomatoes and courgettes alternately onto the skewers, brush with oil. Season and put onto the roasting dish with the lamb cutlets. Bake in oven for 15 minutes.
- Serve with the remaining pesto and new potatoes.