Preheat the oven to 180ºC and prepare a large tray or dish. Select also one large portion of foil, enough to completely wrap the fish and be able to twist the edges. Better than missing.
Wash the vegetables well. Lightly peel the carrots and remove the external or damaged part of the leek. Cut everything in sticks about the same size and have half of the foil in the center (so that the other half can be folded over).
Add an optional drizzle of oil, salt and pepper and add lemon juice, thyme and granulated garlic. Remove and cover with aluminum foil, without tightening, just to cover the vegetables slightly and prevent them from browning excessively. Bake 5-8 minutes.
Remove carefully from the oven. Season the clean sea bass fillets and place one over the vegetables, with the skin down. Cut the other lemon into slices and distribute on top. Cover with the other fish and wrap with the foil.
You have to make a kind of envelope, bending the edges well so that liquid does not escape from inside, tightening the folds but gently not to break or crush the fish. Bake for about 10-12 minutes and open carefully.