Display Screen or Portion Thereof with a Graphical User Interface

Fig. 1 is a front plan view of a first embodiment of the claimed design; and

Fig. 2 is a front plan view of a second embodiment of the claimed design.

The claimed design is the visual features of the display screen or portion thereof with a graphical user interface that are shown in solid lines and gray tones in the figures.

The outermost broken lines illustrate a display screen or portion thereof and form no part of the claimed design. The remaining broken lines illustrate portions of the graphical user interface that form no part of the claimed design. The text features which are blurred in the figures form no part of the claimed design.