There are some suggestions here:
http://uk.answers.yahoo.com/question/;_ylt=Ap5cN5b4PxnNmHr8IUO74UxJBgx.?qid=1006030104632
There are quite a few restaurants down in Cardiff Bay including:
Pizza Express
Cafe Naz and Spice Merchant - Indians
Bistro and Signor Valentino - Italians
Harry Ramsden - Fish and Chips
Pearl of the Orient - Chinese
Thomas - Welsh
Jolyons - Organic
And several more. These are regualrly changing too.
Check out the links below for a better list and some reviews.
http://cardiffbay.uk.com/forumdisplay.php?fid=85