Display screen or portion thereof with a graphical user interface

[0001]FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with a graphical user interface showing my new design;

[0002]FIG. 2 is a front view of a second embodiment thereof; and,

[0003]FIG. 3 is a front view of a third embodiment thereof.

[0004]The outermost broken line rectangle illustrates a display screen or portion thereof and forms 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.

[0005]The stippling in the drawings shows a contrast in appearance.