In a medium bowl, stir together vinegar, black pepper, and red pepper flakes.
Heat oil in a saucepan over medium-high heat. Stir in sesame seeds, and reduce heat to medium. Cook until seeds are brown, about 5 minutes. Remove seeds with a slotted spoon, and stir into vinegar mixture. Mix in cucumber, green onions, and carrot. Cover, and refrigerate at least 5 minutes.