Preheat the oven to 200 ° C top / bottom heat (convection not recommended).
Put the crackers with 1 tablespoon butter and curry in a lightning chopper and chop finely. Wash the fish, pat dry and season with salt and pepper all around.
Place in a baking dish greased with 1 teaspoon butter and cover with the cracked crust. Bake in the hot oven in the lower third for 15-20 minutes until golden brown.
In the meantime, clean the chard. Cut the stalks into 1 cm pieces, cut the leaves into 3 cm strips, finely dice the onion.
Bring plenty of salted water to the boil in a large saucepan. Melt ½ tablespoon butter in another saucepan and sauté the onions over a medium heat for 2 minutes. Dust with 1 teaspoon flour and sauté briefly while stirring. Pour 150 ml of whipped cream and 50 ml of water and bring to the boil. Boil the sauce for 5 minutes, stirring occasionally. Season with salt, pepper, nutmeg and a few squirts of lemon juice.
Cook the chard stalks in boiling salted water for 3 minutes. Add the leaves and cook for 2 minutes.
Drain the chard, drain well and mix with the lemon cream. If necessary, season with salt and pepper and serve sprinkled with lemon zest.