Text Grow and Picture within 'grown' text

[rich2005]

There are any number of how-to's around. Several ways to get a result using Gimp. The only extra, really is a border.

My suggestion goes like this

With the background in place
Add a new layer (with transparency) for the foreground, this can be plain coloured or a pattern or...
Add a new transparent layer for the border.
Add a Letter graphic. this can be a text layer - use some sort of wide font - or adjust it. Consider painting in a letter yourself.
From that letter layer make a selection Layer -> Transparency -> Alpha from selection.
Back onto the border layer and stroke the selection Edit -> Stroke Selection  (with white as the FG colour) make the width 2 x what you want.
Cut out the excess, Edit -> Cut
Onto the Foreground layer and Edit -> Cut again to show the background layer.
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A better way is use a layer mask on the Foreground layer Layer -> Mask -> Add layer mask and use the white option.
Fill the selection in the layer mask with black to show the background layer.

Yet another demo of that procedure:  https://youtu.be/R5s8_nTABR0  duration 4 and a half minutes.