Clean the fennel and cut into very fine cubes. Keep the fennel green.
Remove from the lemongrass the outer hard layers, including the upper four-fifths of the stalk. Bind the outer lemongrass leaves and the stems together with kitchen yarn and place in a saucepan with the coconut milk.
Add the fennel cubes and peas to the coconut milk and cook until soft. Let cool down.
Finely chop the inner, soft part of the lemongrass. Cut the ginger into strips, finely chop the garlic.
Cut the spring onions into thin slices.
Take the cooked lemongrass out of the coconut milk. Add the finely chopped lemongrass, ginger, garlic, lime juice and sugar and season with salt and pepper. Finally mix in the spring onions.
Split the fish fillets into 4 equal portions.
Place a quarter of the fennel pea spring onion mixture in a baking paper. Place the fish on the vegetables, lightly salt and place a lemon thymian stalk on top. Close the baking paper like a candy and tie it with a kitchen string at the ends.
Cook the fish in a preheated oven at 180 degrees, depending on the thickness of the fish fillets in the middle for 15-20 minutes. Arrange the packages directly on preheated plates so that all guests can open their own package.
Serve with white bread for dipping and Pinot Blanc for sipping.