In a small bowl, stir together the feta, sour cream, parsley, tomatoes, garlic, and pepper. Cover and refrigerate for at least two hours (or overnight).
Slice the cucumbers on a slight diagonal into ¼-inch slices. Spoon 1½ teaspoons of the cheese mixture onto each cucumber slice. Arrange on serving platter.
In a small bowl, stir together the basil and olives. Spoon some of the mixture onto each cucumber slice. Serve immediately.