Anything halfway btw Burbank and Irvine?
I'd choose Long Beach, Belmont Shores, or Venice as a halfway point.
For a choices in Long Beach, see, http://chowhound.chow.com/topics/551495
Your suggestion of "doesn't need to be fancy" >> does that mean "nothing expensive" or that you'll eat anywhere with great chow no matter the price or atmosphere?
If you want to spend a little, I suggest Spaghettini in Seal Beach (Long Beach inland), just off the Freeway at Seal Beach Blvd. And, its a destination Sunday brunch, so maybe not what you're looking for? Anyway, really good and fun on Sunday. http://www.spaghettini.com/
There's a place in Sunset Beach you might like for causal/inexpensive
Harbor House Cafe