The main diet of these frogs should be varied as much as possible including crickets, super worms, night crawlers, wax and butter worms etc.
A rodent, chick and even a lizard is an excellant source of protein but should be fed sparingly like maybe 1 feeding every 4-6 weeks.
These frogs have the capacity to eat and process very large prey items. you actually have to limit what you feed them to keep them from becoming obese.
Nothing unusual about an african frog eating an african lizard or an african lizard eating an african frog.
Its as normal as feeding a snake a rodent or a chicken, or a lizard a rodent or a chicken.