Before you start. Preheat the oven to 430°F. Bring a kettle of water to the boil and line an oven tray with baking paper.
Cook the lamb Season the lamb with salt and pepper and coat in the spices. Heat the oil in a frypan over a medium-high heat and cook the lamb fat side down for 3 minutes.. Flip and cook a further 2 minutes, then transfer the lamb to the oven tray and bake in the oven for 10-14 minutes for medium, or until cooked to your liking. Remove from the oven and rest. covered.
Meanwhile, cook the couscous. In a heatproof bowl, combine the boiling water, couscous and a pinch of salt. Stir, cover and leave to swell for 10 minutes, then fluff up the grains with a fork.
Make the Salad. Dice the cucumber and capsicum and crumble the feta. Toss in a bowl with the spinach and vinaigrette.
Finish the lamb. Thinly slice the lamb just before serving.
Serve. Plate the couscous and top with slices of lamb. Serve the Greek salad on the side, drizzling over the tzatziki.