2 tablespoons extra-virgin olive oil, plus more for brushing
Kosher salt and freshly ground pepper
Eight 1/2-inch thick slices ciabatta
6 ounces Manchego cheese, thinly sliced
8 thin lengthwise slices cut from a small red apple
In a food processor, pulse the parsley with the walnuts until finely chopped. Add the 2 tablespoons of olive oil and process until almost smooth. Season with salt and pepper.
Lightly brush one side of each ciabatta slice with olive oil. Turn all of the slices over and top 4 of them with half of the Manchego, the apple slices and the remaining Manchego. Spread the parsley-walnut mixture on the remaining 4 ciabatta slices and close the sandwiches.
Heat a large griddle or skillet over moderate heat. Cook the sandwiches, turning once, until the cheese is melted and the bread is golden brown and crisp, about 5 minutes. Serve at once.