Display Screen or Portion Thereof with Transitional Graphical User Interface

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

1 . 1 : Front, first image in a sequence;

1 . 2 : Front, second image in a sequence;

1 . 3 : Front, third image in a sequence.

The outermost broken lines illustrate a display screen or portion thereof and form no part of the claimed design; the remaining broken lines shown in the reproductions illustrate portions of the display screen or portion thereof with transitional graphical user interface that form no part of the claimed design; the appearance of the transitional image sequentially transitions between the images shown in reproductions. 1 . 1 - 1 . 3 ; the process or period in which one image transitions to another image forms no part of the claimed design.