Chop the chives and chervil, then mix with the olive oil, lemon zest and juice and seasoning. Set aside. Prepare a steamer, brush with oil and place on the heat to boil the water. Roll the sole fillets up into neat little logs and place in the steamer (when the water is simmering), making sure that the final fold is underneath to keep them rolled while cooking. Add the leeks and steam for 3 minutes. Add the asparagus, sugar snaps and broad beans and cook for a further 2 minutes. Carefully remove the fish and vegetables and serve with the herb and lemon oil spooned over the fish.