Object Oriented Perl by Damian Conway is an excellent introduction, not only to OOP in Perl, but to the little features and tricks that make it possible. It will help you in many areas of Perl, not just OOP.
And while a little dated, there is no modern equivalent.
I second this recommendation with the caveat that the book has some advice that I would consider misplaced (like the inside-out stuff) and none of the advanced OO frameworks in Perl existed when it was written. This means a lot of the otherwise excellent code suggestions are (probably) moot for most applications. The enduring strength of the book for me was that it taught me how to think about complicated programming tasks in a much more sophisticated way than I'd been managing on my own and showed me why some of the critique/FUD of the so called "bolt-on" OO in Perl is unfounded.