Heat 1 tbsp olive oil in a pan. Add the onion and cook for 5-7 minutes until translucent. Then add the beans and pour over the stock. Simmer for 5 minutes until the beans are very soft, then whizz in the blender until smooth. Season and keep warm.
To make the salsa, mix together all the ingredients using a food processor or a pestle and mortar. Season to taste and set aside.
Heat a pan and add ½ tbsp olive oil. Cook the lamb for 3-5 minutes on each side until browned and just cooked through.
Spoon the beans onto two plates. Arrange the rocket next to the beans and squeeze over a little lemon juice, if liked. Cut the lamb into thick slices, place on the plates and drizzle over the salsa verde to serve.