Fat Freddy's, 1571 El Camino Real (just off the Santa Ana Freeway at Red Hill Avenue), Tustin. Open Sunday through Thursday, 6 a.m. to 10:30 p.m.; Friday and Saturday till 11 p.m. (714) 832-2422. Also at 2949 Fairview Road, Costa Mesa. Open Sunday through Thursday, 6 a.m. to 11 p.m.; Friday and Saturday till midnight. (714) 545-7713. A '50s-style diner that not only deals in juicy burgers and thick milkshakes, but also serves up a mean blackened catfish, veal parmigiana and more. And there's a jukebox at every booth.