It can be done but your fish selection has to be careful for everyone to live happy.
toothy predators like triggers and puffers are a bad idea. they will nip at and eat mantis shrimp and are one of their main predators in the wild.
lions are bad because they like trying to eat everything. If a lion swallows a mantis, the mantis will likely die, but may also take the fish down with it by smacking around the lion's guts until it kills the fish or is spit out. Both scenarios have happened before. same goes for groupers and other wide-gape predators.
Most wrasses are good choices IMO. I would stay away from the biggest meanest of them since they could injure a mantis. Pseudochromis and dottybacks would probably be good choices too. Maybe tangs if you have a big enough tank?
I also discourage benthic organisms like eels, gobies and shrimp in case you were thinking of them. Stomatopods are benthic foragers after all.
You also have to keep in mind that not all peacocks act the same. some will allow fish to live in peace, others are fish killers. I suggest starting with something you wouldn't cry over losing. a damsel is a good choice as it is fast and sticks to the water column for the most part. My peacock used to take pot shots at fish but the damsel kept getting away so the mantis eventually figured out that fish weren't worth the effort... but it did take a while for it to learn that. At this point I have two wrasses (Halichoeres melanurus and H. chrysus), an anthias (P. squamipinnis), and a blue damsel with my O. scyllarus in a 75g tank with a few LPS corals. note though that O. scyllarus is a deeper water species and will get shell rot if kept under intense lighting systems.
Fish that generally succeed in mantis tanks are diurnal, fast and stick to the water column. Other characteristics help too; for example if they sleep in thee sand like wrasses, that's a plus.
here's a primer to the species in case you haven't found it.
http://www.ucmp.berkeley.edu/arthrop...me=o_scyllarus