Preheat the oven to 180C/350F/Gas 4.
For the lamb, heat one tablespoon of the olive oil in an ovenproof frying pan. Season the lamb medallions with salt and freshly ground black pepper and sear in the pan until browned on both sides.
Place the bread, garlic, lemon zest and juice and cheese into a small food processor and pulse to combine.
Pack the crust mixture on top of the seared lamb slices, transfer to the oven and bake for 5-6 minutes, or until the crust is golden-brown and the lamb is cooked to your liking. Remove the meat from the oven and leave to rest for five minutes in a warm place.
For the creamy leeks and spinach, heat the oil and butter in a frying pan and gently fry the leeks until softened, about 4-5 minutes.
Add the lemon juice and stir, and then add the cream and bring to simmering point. Stir in the spinach until wilted, then stir in the chopped mint.
Serve the blue cheese-crusted lamb on a bed of creamy leeks and spinach on a serving plate.