Price range per person? Any special ambiance? Is it for a certain occasion?
no special occasion, not fancy, just casual that can handle large group.
There are probably several hundred restaurants that fit what you are looking for in the large area you give. All we will be doing is through ing out names, so I guess ill start. Coronado Brewing Co.
mountain mikes pizza
As said there are lots. But the best idea would be to contact them a day or so ahead so they can have tables set up and wait staff assigned. Makes things go smoother.
I'd contact restaurants as soon as possible. 18 is a large group. If you want tables set aside, or you want a special room this will take some advance arrangements. It's like scheduling a luncheon. Will you have people order in advance, or have each person get a menu and order there? 18 separate bills? Oy-vey. Tips can be automatically added for groups of maybe 6 or more. There are tons of restaurant reviews on TA. Maybe you can look at a few and give at least examples of what you consider to be "casual."
If you do an Internet search on "group dining San Diego," "banquet rooms," etc. you may get some ideas.
Been wracking my brain for really good places that could handle a party of 18 given your geographic requests and here is the best I can think of.
Buca Di Beppo is a decent restaurant and good for large groups since they serve family style, they are also decent for catering.
There are a couple of Indian restaurants on Miramar, Taste of India is a good one and they could set up a buffet for your group.
Elijah's near UCSD is nice deli that is pretty big and casual, there is also a Sammy's Woodfired Pizza, which is a lot more than pizza, in UTC and last, since you said Mission Bay, The Atoll at the Catamaran Hotel might work.
We went to Lorna's and that went very well! Sat outside under the heat lamps and it was yummy!
Bucca is in Mira Mesa and will easily do a group that size. You might even be able to get the Pope table for that size. For delivery, Os Kitchen delivers. It used to be called Pat and Oscars.
Mun are you a photographer?
...I took almost that exact photo ;)