In a large enameled cast-iron casserole, heat 2 tablespoons of the olive oil until shimmering. Add the bacon and cook over moderate heat, stirring, until crisp, 7 to 8 minutes. Using a slotted spoon, transfer the bacon to a plate and reserve it for another use. Add the onion and minced garlic to the casserole and cook over low heat until softened, about 5 minutes. Add the piquillo peppers and their liquid and cook for 1 minute. Add the chorizo and the remaining 1/2 cup of stock and bring to a boil. Add the clams, cover and cook over high heat until nearly all have opened, about 10 minutes. Discard any unopened clams. Spoon the stew over the toasts, drizzle with the remaining 2 tablespoons of olive oil and serve right away.