Preheat the oven to 200 degrees and lay a large piece of parchment paper on the counter. Cut the half fennel bulb into very thin slices. Halve the five cherry tomatoes and finely chop the fresh dill.
Distribute the fennel slices in the center of the parchment paper. Place the 150-gram cod fillet on top of this and arrange the halved cherry tomatoes around the fish. Drizzle everything with a tablespoon of olive oil and scatter the fresh dill over the top.
Fold the edges of the parchment paper firmly toward each other to seal, creating an enclosed packet from which no steam can escape. Place the packet on a baking sheet and bake the whole thing for 15 to 20 minutes in the preheated oven.
Remove the baking sheet from the oven when the cooking time is up and the fish is cooked. Carefully open the paper packet to let the hot steam escape. Slide the cod with the vegetables directly from the paper onto a plate to serve.