Step 1

Pound cumin, rosemary, peppercorns, chilli and 1 teaspoon salt in a mortar and pestle, until coarsely ground. Add the lemon and orange zests, then stir in oil. Place lamb in a shallow dish, pour over marinade, then turn to coat well. Cover and refrigerate for 2 hours.

Step 2

Preheat the oven to 200°C. Heat a heavy-based frypan over medium-high heat. In 2 batches, sear the lamb on all sides, turning, for 2-3 minutes. Transfer the lamb to a baking tray, then roast in the oven for 7 minutes for medium-rare, or until cooked to your liking. Set aside to rest for 5 minutes.

Step 3

Meanwhile, for the watermelon salad, whisk together the oil and lemon juice, then season and toss in a large bowl with the remaining ingredients.

Step 4

Stir the mint into the yoghurt and season well. Slice the lamb backstraps and serve with the watermelon salad and minted yoghurt on the side.