Display Screen or Portion Thereof with a Transitional Graphical User Interface

7. Display screen or portion thereof with a transitional graphical user interface

7 . 1 : Front, first image in a sequence

7 . 2 : Front, second image in a sequence

7 . 3 : Front, third image in a sequence

The outer perimeters shown in broken lines in design 7 illustrate a display screen or portion thereof and form no part of the claimed design; the remaining broken lines in the figures illustrate portions of the graphical user interface that form no part of the claimed design; the appearance of the transitional image sequentially transitions between the images shown in reproductions 7 . 1 through 7 . 3 ; the process or period in which an image transitions to another image forms no part of the claimed design.