I definitely agree with Angela K, Rancho has a terrific and delicious range of vegetarian and vegan food. Even though they have a separate vegetarian section on their menu, most of what is in the rest of it can be veganised! There's soy sour cream and soy cheese available for a dairy-free meal. The mock chicken, while not on the menu yet, is a great addition, all you have do to is ask.
I've never ever walked away hungry or disappointed from Rancho. In fact the time I tried the fried soy ice cream I was whatever the complete polar opposite extreme of hungry is. Pretty cheap eats, friendly wait staff, and a cosy atmosphere (downstairs, never eaten anywhere else there) all make for a really solid evening out.
Oh, and the margaritas? Perfect. Get a shaker, you won't be disappointed.