Display Screen or Portion Thereof with a Transitional Graphical User Interface

FIG. 1 is a front view of a display screen or portion thereof with a transitional graphical user interface, showing a first image in a sequence of the new design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof;

FIG. 5 is a fifth image thereof; and,

FIG. 6 is a sixth image thereof.

The appearance of the transitional graphical user interface transitions sequentially between FIGS. 1 - 6 . The process or period in which one image transitions to another image forms no part of the claimed design.

The broken line portions of the display screen and graphical user interface elements form no part of the claimed design.