Put the fish in a bowl, add 1 Tbsp olive oil and the zest & juice of ½ lemon. Marinate for 30 minutes or so.
Heat the oven to 200°C.
Cut the courgette vertically into 4 slices., then place these in a baking dish side by side. Brush with olive oil, season with salt and pepper then add the minced garlic. Bake for 10 minutes.
Take the dish out of the oven. Lower the temperature to 180°C.
Slice the other half of the lemon and put these in the middle of the dish, on top of the courgette. Place the fish on top. Pour over the marinade, scatter the thyme all over and squeeze some more lemon juice on top. Season the fish with salt and pepper. Cover the dish with foil.
Bake for 20 minutes, then remove the foil and cook or grill for 5 minutes or so, until the fish is cooked through and the courgette is golden.
Serve warm.