I assume it's called Onion.7z because it's going to have many layers, not as a reference to TOR.

I was checking the ASCII representation of the binary bits 7-51 of the SHA 1 and 256 hashes of the hint image. Maybe the original image? Anyway, the other problem with my theory is 45 = 9 * 5, so it doesn't break up evenly into bytes, 7-bit ASCII, hex nibbles, or really anything useful.