Preheat the oven to 200ºC. Brown racks on all sides in a hot pan and set aside to cool a little. In a bowl rub together the breadcrumbs, garlic, rosemary, butter and pinenuts.
Brush lamb with mustard and press the mixture onto the meat side of each rack. Put the lamb in a roasting dish and place the tomatoes beside them. Roast for 30 minutes for medium.
Remove lamb, cover it loosely, and rest it in a warm place for 10 minutes before serving. While the lamb rests, put the baked tomatoes in a saucepan and squash with a wooden spoon or masher. Remove any chunky core pieces. Add the stock, extra rosemary and olives and simmer for 5 minutes. Season well with salt and pepper.
Carve each loin in half. Serve lamb with the tomato and olive sauce, roast potatoes and broccolini.