Display screen or portion thereof with a graphical user interface

[0001]FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface according to a first embodiment of the new design; and,

[0002]FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface according to a second embodiment of the new design.

[0003]The outermost rectangular broken line in the figures illustrates a display screen or portion thereof and forms no part of the claimed design. The horizontal dot-dot-dash jagged broken lines indicate symbolic breaks in the display screen or portion thereof, and form no part of the claimed design. The appearance of any portion of the article between the break lines forms no part of the claimed design. The remaining broken lines represent elements of the graphical user interface that form no part of the claimed design. The stippling shown in FIG. 2 depicts a contrast in appearance. The dash-dot broken line, surrounding each of the stippled areas in FIG. 2, represents a boundary line, and forms no part of the claimed design.