Display Screen or Portion Thereof with Transitional Graphical User Interface

FIG. 1 is a display screen or portion thereof with transitional graphical user interface showing a first image of the new design;

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The dot-dash broken lines in the drawings show a display screen or portion thereof and form no part of the claimed design. The remaining broken lines showing portions of the transitional graphical user interface form no part of the claimed design.

The appearance of the transitional images sequentially transitions between the views of FIGS. 1 - 3 . The process or period in which an image transitions to another forms no part of the claimed design.