1. Stir together sugar and cocoa in medium saucepan; stir in evaporated milk. Cook over medium heat, stirring constantly, until sugar is dissolved. Remove from heat; stir in corn syrup. Cool completely.
2. Add yogurt and banana; stir with whisk until well blended. Refrigerate several hours until cold.
3. Pour mixture into 1-quart container of ice cream freezer. Freeze according to manufacturer's directions. 8 servings (1/2 cup each).