We visited the refurbished Tanforan shopping center over the weekend and had a nice lunch at Saigon Cuisine, which is a sit-down restaurant on the floor above the food court. I had a delcious chicken noodle soup and my husband had beef pho, which he also liked. The staff was helpful and gave nice service. My husband tried a drink that consisted of a coconut with an opening at the top where you could drink the milk and scoop out the fruit. Other than BJ's Brewery, I think this is the only sit-down restaurant at the mall. Next door is a Hawaiian place (Aloha Grill?) but you order at the counter.
The food court had some of the usual suspects (Sbarro, Panda) but also had some different offerings, including Thai food and a Japanese place called Sarku (doesn't sound like a Japanese word to me!), which had the longest line. Looks like it's mainly teriyaki. Not all the restaurants have opened. I believe there will be a Mongolian BBQ place.
None of these places are probably worth a special trip, but if you happen to be there and want Vietnamese, try Saigon Cuisine.