Bring the lamb to room temperature before cooking, to help cook quickly and more evenly. Season generously with sea salt and cracked pepper.
Heat a large non-stick frying pan, over medium high heat, add 1 tbsp. olive oil. Cook the backstraps for 4 minutes. Turn. Cook the second side for a further 3 minutes. Remove to a cutting board to rest for 5 minutes before slicing to serve.
Into the pan juices add the tomatoes, season with salt, pepper and a splash of lemon juice. Sauté, shaking pan frequently, until tomatoes soften and skins just begin to wrinkle, about 2 minutes. Into the pan, place the haloumi slices. Cook for 1 to 2 minutes, gently turn and splash with a good squeeze of lemon juice. When golden in colour, remove from the pan and serve on a platter with lamb and tomatoes.