Rinse the fish fillets briefly, pat dry and cut into bite-sized pieces. Drizzle with the lemon juice. Heat the rapeseed oil in a pan and fry the pieces of fish in it on both sides. Season with salt and (coarse) pepper.
Mix the sour cream with the mustard and herbs and add to the fish. Bring to the boil briefly and then season again with salt, pepper and a little sugar.
Rice or baguette goes very well with it and green beans, cauliflower or kohlrabi go well as complementary vegetables.