In a large bowl, toss the sliced potatoes with salt, pepper and enough olive oil to coat them lightly.
Mince the parsley leaves and 2 garlic cloves together finely. (Reserve the parsley stems.)
Take a large baking dish, grease the bottom with olive oil. Line the bottom with about half the potatoes, sprinkle with a spoonful or two of the pecorino cheese, along with half of the parsley and garlic mince.
Season the sea bream with salt and pepper on all sides and inside its cavity. Insert a garlic clove and the parsley stems inside the cavity. Lay the fish in the baking dish.
Now lay the rest of the potatoes over the fish, if you like in a decorative pattern, letting them slightly overlap and covering the body of the fish. Sprinkle the potato covering with the rest of the pecorino cheese, parsley and garlic. Pour a bit of white wine along the side of the dish, just enough to moisten the bottom, then drizzle everything generously with olive oil.
Roast in a moderately hot (190C/375F) oven for about 30 minutes, or until the potatoes are tender and lightly browned on top and the fish is cooked through. .
Remove from the oven and let the dish settle for a few minutes before serving