After a day spent boogie boarding, sight seeing, or visiting the whales at Sea World, you can work up quite an appetite. 
There are plenty of restaurants of all types to satisfy any cravings you may have during your stay. Look at or better yet YELP for restaurants.  Cross reference with this list on YELP for pics and info. 
Breakfast:  Hash House a Go Go in Hillcrest.  Shades in Ocean Beach. The Mission or Broken Yolk in Pacific Beach. Cafe Chloe or Cafe 222 Downtown. 
If you're in the mood for NY style pizza:  Hillcrest has Bronx Pizza. Golden Hill has Luigi'sCiro' Pizza is in the Gaslamp Downtown.

Gourmet Pizza go to Old Venice or the Venetian both in Point Loma.

Burger: Hodad's in Ocean Beach. Rocky's in Pacific Beach. Burger Lounge in multiple locations. Tractor Room in Hillcrest.  

Mexican restaurant: Casa Guadalajara in Old Town.  Taco Shop: La Posta on Washington St or almost any taco shop anywhere in town.

Fish Taco: Wahoo's , several locations. South Beach Bar & Grill in Ocean Beach. Point Loma Seafoods (also best fish and chips) off Scott St.

Cuban Food: Miami Grill in the Golden Triangle. 

Seafood: Oceanaire or Blue Point in the Gaslamp quarter. Roy's in the Golden Triangle.

Upscale Italian: Bice in the Gaslamp Quarter. Cucina Urbana in Hillcrest/Uptown. Old Venice in Point Loma. Buon Appetito or Davanti Enoteca in Little Italy.

Mom & Pop Italian: The Venetian in Point Loma; Filippi's, several locations, but the Downtown location on India street is better than others.

Mimmo's Italian Village on India Street offers attentive service and a diverse menu in a surprising Venetian St. Mark's Square venue. Starters include a delightful fruit, cheese and meat platter. Salads, Italian subs, eight gourmet pizzas and homemade pastas all please.

Chinese:   Mandarin House in Hillcrest; Schzechaun Mandarin on Mission Gorge; Panda Inn in Horton Plaza.

Sushi:   Kappa Sushi in Scripps Ranch on hibert St.  Ono Sushi in Hillcrest; Cafe Japengo in the La Jolla Village/Golden Triangle area;Cheap stuff: Ichiban in Hillcrest on University Ave.  Half-price rolls happy hour between 3 and 7pm, Mon-Fri. 

Thai: Thai House in Convoy in Kearny Mesa. Amarin Thai in Hillcrest. 

Steak: Ruth's Chris in either Del Mar or at the San Diego Harbor; or if you think you can cook your own, The Strip Club  in the Gaslamp.

Persian: Bandar in the Gaslamp.

Sandwich: Cappriotti's in Mission Valley; EZ Jays in Pacific Beach; Chez Nouz in the Miramar/Mira Mesa area.

Asian Fusion: Red Pearl Kitchen in the Gaslamp; Roppongi on Prospect in La Jolla

Flavor Fusion:  Indigo Grill in LIttle Italy. Southwest and Pacific American Indian

Great for Kids: Corvette Diner in Point Loma @ Liberty Station. A very fun and loud 50's themed restaurant.