Simply put all of the ingredients, apart from the olive oil, into a food processor and whiz, add the oil in a slow steady stream until you have a creamy green sauce. Set to one side and let the flavours start to develop. This can be made a day or two before and kept in the fridge.
Steam the new potatoes until tender. Meanwhile brush the lamb cutlets with a little olive oil, rub with the garlic clove and sprinkle with salt and pepper, grill for a few minutes on each side until cooked to your liking.
When the potatoes are cooked place them into a large dish with a few drops of the olive oil and crush briefly with a fork; the potatoes should be slightly broken – not mashed.
Add the chopped herbs, lemon juice, salt, pepper and a little more olive oil. Stir with a wooden spoon until all the ingredients are combined.
Serve the lamb on warm plates with crushed potato, fried red onions and drizzle with the pesto.