Grease a baking tray. Wash the fish, dab dry and place on the baking tray. Cover fish with foil and cook in a preheated oven (electric cooker: 80 °C/ convection oven: not suitable °C/ gas: not suitable) for 15-20 minutes.
Clean, wash and drain the spinach. Clean, wash and slice the mushrooms. Peel and chop the onion. Peel and slice garlic. Cut open the vanilla pod and scrape out the pulp.
Use pod for other purposes. Heat the oil in a large pan. Sauté the ginger, vanilla pulp, onion and garlic until transparent. Add the spinach, mushrooms and stock and fry for 2-3 minutes, turning until the spinach has completely collapsed.
Melt 1 tablespoon butter in the spinach, season spinach with chilli salt and nutmeg. Heat 2 tablespoons of butter in a small pot until it is brown, remove from heat. Take out fish, remove foil, season with red-green chilli salt and arrange on plates with spinach.
Spread fish with liquid brown butter.