Display Screen or Portion Thereof with a Graphical User Interface

FIG. 1 is a view of a display screen or portion thereof with a graphical user interface; and,

FIG. 2 is a second view thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 and 2 . The process or period in which one image transitions to another image forms no part of the claimed design. The outermost broken lines show display screen or portion thereof and form no part of the claimed design. The broken lines within the figures show portions of the of the graphical user interface and form no part of the claimed design. Although the broken lines may include various styles or thickness, no broken lines form part of the claimed design.