UserParameter=my.param[*],awk '$11 == "foo"

{ bar=$5} END {print bar}'

even if only called with one parameter zabbix replaces any occurence of $1, $2, $3......

i believe zabbix should not touch at least single-quoted strings, so that i could use:
UserParameter=my.param[*],awk '$11 == "'$1'" { bar=$5}

END

{print bar}

'

and $1 would get replaced as it is not in quotes, and i could still use $1,$2... in awk syntax