Adjust a rack in the upper part of an oven and preheat to 325 F. In a food processor, fitted with its metal blade, or in a blender, combine the capers, garlic, sardines and oregano oil. Process until blended. Add the olives and pulse to obtain a coarse puree. Taste for seasoning and transfer to a small bowl. Using a zester, or a small shredder, and holding the lemon over the olive puree, shred the zest, yellow part only, from the skin of the lemon directly onto the puree. Brush bread slices lightly on both sides with oregano oil. Place on a baking sheet and toast in the upper part of the oven until lightly toasted, turning once, about 10-12 minutes. To serve: Arrange crostini on a serving plate with the bowl of olive spread.