1. Peel and chop the onion and garlic. Sauté them with a teaspoon of oil in a large skillet over medium heat until golden. Add the crushed tomatoes and thyme, season with salt and pepper, then let it simmer over low heat for 5 minutes. Set aside and let it cool.
2. Cut a slit in the thickness of the fish and fill it with the tomato mixture. Wrap it with a slice of smoked bacon. Secure everything with kitchen twine.
3. In another skillet, brown the cod fillet rolls with 1 teaspoon of oil over very low heat until golden. Remove them from the skillet and place them in a dish covered with aluminum foil.
4. Wash the zucchini, peel the carrots. Grate them using the coarse side of a grater. Heat the remaining oil in the same skillet used for the cod fillet rolls and sauté the vegetables over high heat for about 5 minutes.
5. Add the lemon zest, salt, and pepper. Place the cod fillet rolls on top of the vegetables and cover. Let it cook for another 5 minutes over very low heat. To serve, remove the twine and sprinkle some chervil leaves.