The best food is either at the Parque or in the restaurants nearby.
You can satisfy your need for USA-style food from
Subway
Tip Top
RostiPollo
On The Run
Hotel de los Volcanes
La Union grocery store
Pizza Maria Best in Chinandega by far
There is also great food from the many fritangas on the side of the road.
Also, do not forget to try TONCUA! It is the most delilious fruit ever. Ask street vendors if they know anyone who is selling Tonqua.
The best pizza in Nicaragua comes from Pizza HOT... love the name, but love the pizza more. There are 2 Pizza Hots in Chinandega!
If you want gourmet food, check out Jack's, which is on main street.
Just ask everyone for directions to these various places because they will know.