Living in SoCal, we have baja-style fish tacos all time.
It took me a long time to figure out what that beautiful white sauce is. It's Mexican crema. If you have a latino market nearby, go there and get it, it's worth it. If not, creme fraiche works just about as well. Google recipes will tell you some mayo and sour cream mixture with chipotles and crap. Don't do it. It's a simple fisherman's dish. Go with the crema.
Beyond that, I agree with Gordon - go with Soft corn tortillas, shredded cabbage, ciliantro, lime, and crema. For the fish, beer battered and fried is delicious, but we usually cook white fish on the grill in a foil packet (salt, pepper, and lime slices on the filets) for 10 minutes. Cod will do fine, though it gets tough fast. Mahi mahi is great, so are red snapper and tilapia.
Beer recommendation? I had gose with mine last week and it was amazing. Pre-pro lager is also nice, as well as any light lager.