Place the cod in an oiled oven proof dish. Place a basil leaf on each cod loin. Place a slice of mozzarella on each cod loin.
Slice the tomatoes in half and place on and around the cod. Sprinkle over the Parmesan cheese and season with salt and pepper(be frugal with the salt as the parmesan is salty). Drizzle with a little Olive Oil.
Bake for 12-15 minutes until the cheese is bubbling and the fish is cooked.
While the fish is cooking make the basil oil. Tear the remaining basil into a pestle and mortar, add a pinch sea salt and freshly ground black pepper and the extra virgin olive oil and crush to a fine paste.