Question on chown in parallel - eviltoast

Hello I am seeking a simple solution to running a list of “chown -R” <mydir>" commands in script.sh

It takes a long time to sequentially execute all of these chown commands recursively because the directories have so many files. I want to be able to tackle the root level directories in parallel to speed things up. I imagine there must be a simple way to do this while keeping the list of commands in a single file. xargs and some of the other things I saw online looked like bad fits or would be over engineering this problem.