How to create minimum size (empty) zip file, which has 22B?

Here you go:

50 4b 05 06 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00

That has the MD5 signature you provided.

If you have Info-ZIP's zip, you can create it thusly:

zip empty.zip anyfile
zip -d empty.zip anyfile

That adds "anyfile" to a new zip file, and then deletes it from the zip file, leaving it empty.

An easier-to-use version for copying-and-pasting into the shell:

echo UEsFBgAAAAAAAAAAAAAAAAAAAAAAAA== | base64 -d > empty.zip

This just prints the base64'd version of the empty zip file (created by creating a zip file with a single file then deleting that single file from the zip file), and reverse the encoding with base64 -d and writes the output to empty.zip.

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If the version of base64 that ships with your machine doesn't use the same syntax as above, here's a more-portable but less-terse alternative:

echo UEsFBgAAAAAAAAAAAAAAAAAAAAAAAA==  | openssl enc -d -base64 > empty.zip