Preheat oven & make the gratin. Preheat the oven to 375 degrees F. In a small food processor, blitz the garlic until minced. Add the nuts and herbs and pulse until the texture is a coarse, crumb-like texture. Next, add the cheese and pulse until just combined. (Do not over pulse to avoid making the mixture pasty). Dump the mixture into a small bowl and add the olive oil, salt, and pepper. Mix well.
Pat the cod dry with a paper towel. Place the fish pieces into a baking dish and season them with salt, pepper, and olive oil. Top each piece with a couple of spoonfuls of the gratin mixture.
Place the dish on the middle oven rack. Bake for 9-15 minutes or until the internal temperature of the fish is at least 145 degrees F and the gratin is lightly golden brown. Serve with salad and enjoy!