Add the vinegar to a blender, replace the lid, turn it on, and through the feed tube add, 1 at a time, the garlic, crushed red pepper, salt, and black pepper. Leaving the blender running, add the olive oil in a slow thin stream. Set aside until needed.
Toss the greens, olives and cucumbers together with enough dressing to coat. Fold in the feta cheese. Serve additional dressing on the side.