1.In a large bowl combine soy sauce, mirin, lime zest and juice and sugar.
2.In a second bowl, combine seafood and pour 1/3 of the soy sauce mixture over.
3.Heat oil in a large saucepan on high. Cook ginger and garlic for 1 minute, until aromatic. Stir in stock, water, fish sauce and reserved soy mixture. Bring to the boil. Add kumara. Simmer for 3 minutes.
4.Add undrained seafood to the pan and gently stir. Cook for 2-3 minutes, until mussels open (discard any that do not open). Add spinach and simmer, uncovered, for 1 minute, until spinach wilts. Serve topped with sliced green onion.