Display screen or portion thereof with a graphical user interface

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The dashed broken lines around the Figures show a display screen or portion thereof, and form no part of the claimed design. The dot-dot-dash broken lines and the areas within the dot-dot-dash broken lines shown in white overlay form no part of the claimed design. The dot-dash broken lines and the areas between the dot-dash broken lines and the dashed broken lines shown in white overlay show environment that forms no part of the claimed design.