I don't think this is a particularly wise idea, given the nature of the beasts. Lionfish will eat pretty much anything that will fit in their mouths, up to about 2/3 of their size. This means that a 4" dwarf lionfish will likely at least try to have a medium-sized mantis (2-3") as a snack.
On the other hand, given that lions are ambush predators, the are relatively slow and hang out near the bottom for extended periods. This is dangerous for the lion if the mantis is anywhere near the same size (or larger) than the lion.
Try fish that stay up in the water column (like damsels, including clowns) and avoid fish that like to sit on the bottom and/or eat shrimp (so no hawkfish, blennies, gobies, jawfish, wrasses, triggers, etc). If you want a "tough" fish, it's hard to beat a tomato clownfish. I had one that sometimes drew blood when I cleaned the tank! Needs at least, like, 30 gallons, though, they get pretty big.
Have fun,
Dan