Remove the crusts from the toast and grate finely between both palms. Peel ginger and chop finely. Mix egg yolk, toast bread crumbs, ginger and lemon juice.
Wash the fish, dab dry and cut into 4 equal pieces. Prepare rice in boiling salted water according to package instructions. Peel and finely dice the onion. Heat 1 tablespoon of oil in a saucepan.
Sauté onion in it, add deep-frozen spinach and 2-3 tablespoons of water. Cook on low heat for 16-18 minutes. Season to taste with salt, pepper and nutmeg. Stir in cream.
Heat 2 tablespoons of oil in an ovenproof pan, fry the fish fillets in it until they are hot. Spread the crust evenly on top. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 5 minutes.
Drain the rice. Grease 4 timbal moulds (alternatively cups). Fill the rice into the moulds and press down gently. Turn the rice out onto plates and arrange with the spinach leaves and the fish fillet.
Sprinkle with coarse pepper and paprika powder.