Find list of directories one level deep from matching directory

Just add a -prune so that the found directories are not descended into:

find . -type d -path '*/wp-content/plugins/*' -prune -print

You need to quote that *wp-content/plugins/* as it's also a shell glob.

If you want only the directory names as opposed to their full path, with GNU find, you can replace the -print with -printf '%f\n' or assuming the file paths don't contain newline characters, pipe the output of the above command to awk -F / '{print $NF}' or sed 's|.*/||' (also assuming the file paths contain only valid characters).

With zsh:

printf '%s\n' **/wp-content/plugins/*(D/:t)

**/ is any level of subdirectories (feature originating in zsh in the early nighties, and now found in most other shells like ksh93, tcsh, fish, bash, yash though generally under some option), (/) to select only files of type directory, D to include hidden (dot) ones, :t to get the tail (file name).

You could have find recurse, sort of:

find / -type d -path *wp-content/plugins -exec find {} -maxdepth 1 -mindepth 1 -type d \;

Bash-ically:

shopt -s globstar
printf "%s\n" **/wp-content/plugins/*

prints:

bat/bar/foo/blog/wp-content/plugins/GHI
baz/wp-content/plugins/ABC
baz/wp-content/plugins/DEF
foo/bar/wp-content/plugins/XYZ

or

shopt -s globstar
for d in **/wp-content/plugins/*; do printf "%s\n" ${d##*/}; done

prints:

GHI
ABC
DEF
XYZ