Pre-heat oven to 220 °C, 425F, Gas Mark 7. Mix together the breadcrumbs, Lamb Mint & Rosemary Seasoning, lemon juice and oil and press onto the fat side of the lamb. Place in a small roasting tin and bake for 20-30 minutes for a rare to medium appearance, or 30-35 minutes for well done.
Meanwhile, blend the cornflour with the remaining ingredients in a small saucepan. Bring to the boil, stirring until thickened. Serve with the lamb.