Wash the carp and pat dry. Drizzle some squeezed lemon juice inside and outside. Let stand for 15 minutes. Pat the carp dry again and season with salt and pepper.
Slice the tomatoes, red peppers, green bell peppers, and onions into rings or slices. Stuff the belly of the carp with a bunch of parsley and add a pinch of salt.
Pour the oil and 80 g butter onto a baking tray. Preheat the oven to 180 °C (356 °F).
Brush the carp with the beaten egg on all sides, then coat thoroughly with the ground almonds.
Place the carp on the tray and moisten it completely with the hot oil and butter. Arrange the vegetable slices around the fish and season with salt and pepper.
Bake at 180 °C (356 °F) for 15 minutes, then reduce the heat to 150 °C (302 °F) and bake for another 25 minutes.
Turn the vegetables over. Spoon the pan juices over the fish. Five minutes before the end of cooking, season the carp with salt, drizzle with the remaining squeezed lemon juice, and top with the remaining butter strips.
Add 1/2 bunch of parsley (plucked from stems) to the vegetables. Stir the sour cream and 6 tablespoons of water into the pan juices.
Serve the carp and vegetables from the tray, garnished with lemon wedges and fresh parsley.