Preheat the oven to 180°C/gas mark 4. Put the fish on a large, lightly greased baking tray and cut four slashes on the top of each one. Add the sliced lemon, tomatoes, olives and most of the rosemary sprigs, and drizzle with 1 tbsp oil. Season with pepper and roast for 10-15 minutes, until the fish is cooked and the skin is crisp.
Meanwhile, in a large pan, heat the remaining olive oil over a medium heat. Chop the remaining rosemary leaves, add to the pan and cook for 30 seconds. Stir through the butter beans, 50ml hot water and the lemon zest and juice. Cook for 2-3 minutes until warm, then crush using a potato masher. Season with black pepper and serve with the roasted sole.