Display Screen or Portion Thereof with a Graphical User Interface

The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the Office upon request and payment of the necessary fee. FIG. 1 is a front, perspective view of a handheld computing device with a display screen or portion thereof with a graphical user interface showing our new design; and, FIG. 2 is a front view thereof. Broken lines in FIGS. 1 - 2 show portions of a computing device with the display screen or portion thereof and form no part of the claimed design.