We like the Seafood Grill across from the train station. Fresh fish, grilled, or in fish tacos. Avoid the fried stuff - oysters, etc. Also, in the same little center is Kentro, a new Greek place that is very good.
For Mexican, try El Camino Real, on Euclid, south of Chapman, in the Stater Bros center.
El Camino Real, 303 S Euclid Avenue, Fullerton
Seafood Grill, 100 S Harbor Blvd, Suite D, Fullerton
Kentro, 100 S Harbor Blvd, Suite A, Fullerton
Camino Real Restaurant
13756 Amar Rd, La Puente, CA 91746
100 S Harbor Blvd Ste D, Fullerton, CA 92832