I found the picture of a microwave, cropped it to get a closer focus on the microwave itself, selected it using the pen tool.
Selected window, copied it separately and deleted the center. Added the fish tank environment, resized it to match the size of the window, softened edges, added fish, added the window on top, changed blending mode to linear light and lowered opacity under 50% to get a better transparent look.
Colored the microwave using color balance and hue/saturation, added bubbles, fish and sea horse on the exterior. Added bubbles inside as well.
Added shadows and lights using adjustment layers and gradient tool.

Thanks to David for bear and salmon pictures.
I'm very new to this , I've only had PS about 7 months and was so intemidated by it. I've just now two months ago have been teaching myself how it works. I'd like to give a BIG thanks to all the talent out there for making Tutorials. Thats the only way other than really screwing up on a trial and error basis that I have gotten this far. It's hard for me to remember what I do but , but mostley its just cut and paste on layers using a soft large brush, and some dodging and resizing. I hope to get to where I really understand PS as well as some of you. I'm in AWE at some of the things I see being done with it. Totally amazing!

Remember its an acorn. A light hearted starter to the reborn PST.

Cropped and lightened the acorn tip and changed the hue and sat and added a bit of red to the end.