I am not sure. I know you can't from what I have read about Carnival. If you go to www.cruiseclues.com they have a list of menus from most ships including the Mariner. It will kindof get your tastebuds a rolling!!!
"The philosophy of one century is the common sense of the next."
Yes, you may order hot items on RCCL - egg dishes during breakfast time, and even off the dining room dinner menu during dinner hours. Off-times, however, (e.g., midafternoon, after 9 p.m.) you can usually only get cold offerings.