Wash lemons hot, dab dry and cut into thin slices. Clean and wash the zucchini and spring onions. Cut the courgettes into slices and the spring onions into pieces. Wash thyme and shake dry. Rinse fish cold, dab dry and cut into 4 equal pieces.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Quarter each baking paper crosswise. Arrange vegetables, 1 piece of fish and lemon slices, up to 4 pieces each, in the middle of the paper quarters. Drizzle with olive oil, season with salt, pepper and thyme. Place each paper over the filling and form into packets, wrapping them with kitchen string as desired. Cook in a hot oven for about 20 minutes.
Drain the capers. Peel sweet potatoes and cut into 1-2 cm cubes. Heat the oil in a large frying pan. Fry the potatoes for about 15 minutes, turning them carefully. Season with salt. Add remaining lemon slices and capers and fry briefly.
Meanwhile prepare the Blitz-Hollandaise, heat 125 g butter for this. Squeeze the orange, grate the peel finely. Whisk egg yolk, vinegar, orange peel and orange juice in a tall beaker with a hand blender. Mix in hot butter in a thin stream. Season to taste with chopped parsley and cayenne pepper. Remove fish parcels from the oven and place on plates. Potatoes and sauce
Potato decoration: Cut out 1 star (approx. 4 cm) from 4 sweet potato slices. Fry both the stars and the remaining potato rings and arrange them on the plates as decoration.