In a large saucepan, heat the oil with the garlic over moderate heat. When the garlic sizzles, add the fish stock, wine, and oregano. As soon as the liquid comes to a boil, add the clams and cover the pan. Steam the clams until all of them have opened, 3 to 5 minutes; discard any unopened clams. With a slotted spoon, remove them from the pan and keep them warm in a covered bowl. Stir in the remaining ingredients, except the black pepper, into the liquid in the pan. As soon as the liquid returns to a simmer, place the clams, shells and all, on top of pasta and spoon the liquid over them. Season to taste with black pepper.