Display Screen or Portion Thereof with a Graphical User Interface

FIG. 1 depicts a front view of a display screen or portion thereof with a graphical user interface showing a first embodiment of our design; FIG. 2 depicts a front view of a display screen or portion thereof with a graphical user interface showing a second embodiment of our design; FIG. 3 depicts a front view of a display screen or portion thereof with a graphical user interface showing a third embodiment of our design; FIG. 4 depicts a front view of a display screen or portion thereof with a graphical user interface showing a fourth embodiment of our design; and, FIG. 5 depicts a front view of a display screen or portion thereof with a graphical user interface showing a fifth embodiment of our design. The broken lines showing the display screen or portion thereof with a graphical user interface illustrate portions of the article and form no part of the claimed design.