Where is a good place to eat dinner in San Francisco near Union Square?

Kind of depends on what type of food and ambiance you want. Check out reviews on yelp for any fo the following restaurants
Bistro Scala
Kulettos
E&O Trading Company
Cesarios
Lori's Dininers
John's Grill
Cafe Claude
Ploof
Henry's Hunan on Natoma near the MOMA
There is a huge food court with some upscale options in the Westfield Shopping Center at 5th and Market.

Skip the cheescake factory it is a zoo and they don't take reservations

actual, the eating places in union sq. suck...thats only my opinion. Do you like cuban nutrition? Cha cha cha's interior the undertaking takes reservations and that they have got dazzling tapas and sangria! it rather is a huge relaxing, tasty, and low priced place to bypass!

The Garlic Rose