SLO eats well for a small city. Cal Poly keeps standards honest — students aren't a patient or wealthy crowd, so places that don't deliver value tend not to last. The downtown restaurants cluster around Higuera and Monterey Streets; most of them are within a few blocks of each other and you can walk between options if you change your mind.
The local food culture leans California: fresh ingredients, menus that change with the seasons, and a fondness for farm-to-table language that is, in this case, backed up by actual proximity to farms. San Luis Obispo County produces Edna Valley wine, good dairy, and vegetables year-round. You'll find that showing up on menus all over town.
For something outside the ordinary, drive down to the Madonna Inn. The Gold Rush Steakhouse is campy and fun, and the pink-and-gold dining room is part of the experience.