I am under the impression that Esperanto allows both manĝas and manĝu here, as using either doesn't really affect the meaning.
In this way you can use whichever makes most sense to you, no matter what your mother tongue happens to be. (Zamenhof allowed for some "wiggle room" for cases such as these.)
Just be aware that the other way is also considered valid Esperanto. So when you encounter it, accept it as valid (despite the fact that it is not how you would normally say it) and you should do fine.