Display Screen or Portion Thereof with Transitional Graphical User Interface

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

1 . 1 : Front

1 . 2 : Front

1 . 3 : Front

1 . 4 : Front

1 . 5 : Front

1 . 6 : Front

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.