Display screen or portion thereof with transitional graphical user interface

[0001]1. Display screen or portion thereof with transitional graphical user interface

[0002]1.1 : Front

[0003]1.2 : Front

[0004]1.3 : Front

[0005]1.4 : Front

[0006]1.5 : Front

[0007]1.6 : Front

[0008]The outer perimeter shown in broken line in the drawings illustrates a display screen or portion thereof and forms no part of the claimed design; the remaining broken lines in the drawings illustrate portions of the graphical user interface that form no part of the claimed design; the dot-dash broken lines define boundaries of the claimed design and form no part thereof; FIG. 1.1 is the image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design; FIG. 1.2 is the second image thereof; FIG. 1.3 is the third image thereof; FIG. 1.4 is the fourth image thereof; FIG. 1.5 is the fifth image thereof; and, FIG. 1.6 is the sixth image thereof; the appearance of the transitional image sequentially transitions between the images shown in FIGS. 1.1-1.6; the process or period in which one image transitions to another image forms no part of the claimed design.