Generally, I like this picture. To be really nit-picky, if it could have been framed so that more of the blue and white showed at the bottom as well, or none at the bottom it would have had more balance for me.
i know exactly how you feel ... you could also have done soup to nuts. more comment. i think the lighting could be a LOT better to take advantage of the great subject. ask me later in the forums and ill be more specific.
Not sure why you chose to photograph the onion upside down. It seems the rotting is on the bottom, and flipping around the onion would've displayed more of your intended purpose.
Personally I think maybe if the board was pushed up a little more so that the blue checker showed on the lower half and the book was out of view it stand out more.
composition needs some work to clear out the clutter in the frame, e.g., the book, the bit of something other than onion on the chopping board etc. Light is a bit flat too which doesn't make it very interesting - maybe sunlight/ daylight would have brought out some textures/ shadows ?
Interesting interpretation of the challenge though.
ack, my eyes are tearing. The angle is too high. In the future try to get a lower angle and fill the frame with your subject. You'll get a much nicer shot that way. I think I understand what you were thinking for your transition but I don't like it.
I like photos that tell a story. This one does that. But I feel the composition could be improved. Maybe fill the frame with the onion. Or show some sliced with the rot? Lot of possibilities.