How to Make It
Gently press the crushed pepper into the beef and sprinkle with the salt. Heat 1 tablespoon of the olive oil in a medium skillet. Add the beef and cook over high heat until well browned all over, about 10 minutes. Let cool, then refrigerate until chilled, at least 2 hours or for up to 2 days.
Preheat the oven to 350°. Brush the bread slices lightly on both sides with the remaining 2 tablespoons olive oil and arrange them on a large baking sheet. Bake for about 7 minutes, turning once, until lightly browned.
Spread about 1/4 teaspoon of the tapenade on each toast and set a halved arugula leaf on top. Using a sharp, thin-bladed knife, cut the chilled beef against the grain into 24 very thin slices. Arrange a slice of beef on each crostini and serve.