Preheat the oven to 325° degrees Fahrenheit (160° C). Pat the lamb dry with paper towels and then coat with a thin layer of oil. Season with salt and pepper.
Next, preheat an oven-proof, stainless-steel pan over medium- to medium-high heat. Once the pan is heated, add the oil and then place the lamb presentation-side down. Let it cook for about 2 or 3 minutes, until the underside is golden. Then flip and cook for another minute or so on the other side.
Transfer to the oven for approximately 10 to 15 minutes. Ultimately, this will depend on size of the sirloin and how you like your lamb cooked. Lamb sirloin is quite lean, so it is best served medium-rare.