1. Preheat the oven to 200 °C (392 °F). Clean the vegetables. Finely slice the fennel using a mandoline. Cut the tomatoes in half and slice the lemon. Mix all the vegetables with oil. Season generously.
2. Cut a rectangle of parchment paper. Place the vegetables on it and then the seasoned sea bass.
3. Cover with a second sheet of parchment paper and fold the edges carefully to seal the parchment packet. Bake for 30 minutes.
4. Cook the rice according to the instructions on the package.