I always try to find a place that's easy to get to from the freeway so that my valuable visiting time isn't spent talking on my cellphone trying to get un-lost. That being said there are great convenient choices between LA and SD.
In San Clemente:
The Vine: Wine Country Cuisine. http://www.vinesanclemente.com/
Further north on the 405 & 22
Brodard Chateau You can see it off the freeway and now that construction on the 22 is mainly done traffic shouldn't bee too bad. Vietnamese. Nice upscale atmpshere
By South Coast Plaza at the Bristol St. exit (but south/west side of the freeway, not toward the mall) in The Lab Anitmall is Habana. Arty atmpshere and good food.
2nd Street in Long Beach (Belmont Shore area) has lots of restaurants. It's been awhile since I lived up there so I don't know what's good anymore but that's a nice meeting location.
All these choices (except Brodard) locate you in nice pedestrian areas so that you can walk around and carry on the conversation after dining and all of them are easy to find and freeway close.
I like Laguna Beach but there is only one way in (Laguna Canyon, 133) and if there is traffic you're stuck. Also, parking down there is almost impossible on the weekends. We live close and hardly ever go there because it's such a pain. It is pretty though. Maybe a good LB location would be The Montage, that way you can valet park and not worry about feeding the meters or getting a ticket. The Loft is their casual restaurant. I had a really good breakfast there recently (although breakfast for two, no booze, was about $75). You can also eat at Mosaic by the pool. I had a really pricey chardonnay there once. This location is not for the pocketbook challenged.
It doesn't get much prettier that this location in Southern California though.
Pate's got this one pretty much nailed down. San Clemente/Dana Point/San Juan is the half-way point and those recs are all good. If you want some more popular priced choices I'd add Mongkut Thai, Beachfire and Sonny's (in San Clemente) and Mario's Cucina, Ciao Pasta or Sun-dried Tomato in San Juan. (maybe Cedar Creek too). If it's early and you want something casual and beautiful, we love the bar side of Fisherman's Restaurant on San Clemente Pier (NOT the restaurant side) - right on the water, good drinks, so-so bar appetizers but good chowder, clams and oysters. At sunset, this is what SoCal living is all about.
How about Taco Rosa in Newport Beach? They have great mixed drinks made with real fruit juice and a decent menu. I would recommend the Newport Beach location over the Irvine location because the Irvine location is more busy and crowded.
2632 San Miguel Dr
Newport Beach, CA 92660
Althogh I prefer Taco Rosa, a friend of mine loves Javier's.
480 S Coast Hwy
Laguna Beach, CA 92651
I often meet a friend from SD in Laguna Beach. We've found that it's a nice halfway point between LA and SD, and there are a variety of restaurants and coffee houses to choose from there. I also think places in Tustin, Newport Beach or Irvine could work for you.
I'm always recommending Bistango in Irvine if you're in the area. Live Jazz piano lounge or a solo guitarist, extensive wine list, best chocolate or grand marnier souffle. Food is reliably good. They have really infused and combined art, music and dining and style into one excellent blend. Have fun!
A place that I had a great dinner at awhile ago in Torrance was Restaurant Christine. Quite a bit off the 405, but worth a look. Chef came out and chatted with us a little while and sent out a complimentary amuse bouche. Relaxed atmosphere, really enjoyed our experience there.
If you've got money to burn and/or it's a special occasion - Roy's in Newport Beach is fantastic.
Otherwise, I recommend Taleo in Irvine (405/Jamboree). Great sort-of-upscale Mexican. Very nice, California-casual place, some outside seating. All the food is great; fantastic queso fundido and guacamole.
Lastly, maybe Opah. They're in Irvine, Aliso Viejo, and Rancho Santa Margarita. I've always had really great meals at Opah in Irvine.
Great great ramen not quite half way down at Shin Sen Gumi Hakata ramen on Redondo beach blvd, i have take non foodies there before, they can enjoy without thinking of it as exotic, just a dolled up version of top ramen. Top Baguette or any one of a number of other Vietnamese places in Westminster (Bolsa Ave) are all very good. In DelMar i had a great meal at a place on the water. I think it was called Jakes. A real wood on the walls, fancy Sandiego county steak house, i did not expect the food to be standout, but it was. Not cheap.