Chontaleño cheese is originally from Nicaragua but can be found extensively in Mexico and in Mexican cuisine. This is a salty, semi-firm cow's milk cheese typically used for grating. You can find this cheese smoked too and it is referred to as Chontaleño Ahumado.
Grate the cheese and use it on anything you'd like to add a little salty, milky flavor like
Most likely you'll need to find this in a grocer that is well-stocked with Mexican cheeses; otherwise find in your local Mexican tienda if you have one. One good producer of the cheese in California is Peluso Cheese in Los Banos, California. They are famous for their fabulous (Teleme cheese) but they also produced a line of Mexican cheese too.
Although food purists might say there is no good substitute for Chontaleño; in a pinch you could use one of the following alternatives: