Wow, this is fabulous! I made a few changes to suit my personal tastes and it was still an absolute winner. My changes included: using ciabatta bread, using portabella mushrooms, and omitting the black olives. I also made a different sauce by heating red pepper flakes in olive oil, draining, and then mixing with prepared ranch dressing. The best word for these paninis is YUMMY!
More about this perfect panini it doesn't need any other ingredients; it's perfect as it is, doesn't make you wish for anything else added.