Can anyone suggest a moderately priced restaurant near the La Isla mall on a Sunday night.

Why not "in" La Isla Mall? There are quite a few. You have everything from Johnny Rockets, Chili's, McDonalds, Starbucks, Cold Stone Creamery to upscale restaurants.
What are you looking for?
Cheryl
We are looking for someplace which is not a chain or a location we can go to here in MN. Something more local.
There are many restaurants in Isla mall that are not chain restaurants that overlook the lagoon.
There are over 300 restaurants in and around the hotel zone within a few minutes bus ride of La Isla or in La Isla Mall. There's pretty much everything - chains (American and Mexican) and local restaurants, every type of cuisine. You'll need to specify what you're looking for - Yucatean cuisine? Italian? Mexican? Seafood? Steak? Thai? etc. What is "moderate" in price to you?
Almost too many options to even recommend something.....
Cheryl
I'm not sure what "moderately priced" means to you, but here are some non-chain restaurants in that area that I love:
Fish Fritanga: located next to La Isla, very authentic Mexican seafood right by the lagoon (tons of friends recommend it as well), $20 - $30 dollars per person
Thai Lounge: located at La Isla, more expensive but very much worth it, $50 - $60 per person, Thai cuisine, on the lagoon, really amazing atmosphere that you can't get anywhere else
I really enjoyed the street tacos at Taco Grill inside La Isla. I don't remember their specific prices but 5 of us ate there, all of us had a few alcoholic drinks, a couple appetizers, our tacos and it was roughly $75. The restaurant overlooks the lagoon.
I'd second El Fish Fritanga....good beachy restaurant walking distance to La Isla Mall and definitely get you into the vacation mode!
Hard to find...look for Domino's pizza sign on Lagoon side, follow stairs around back to restaurant.
I had El Fish Fritanga on my list....will we need a reservation for a Sunday night?
We've eaten there about 5-6 times in the past year (including 3 times 2 weeks ago) and have never made reservations. If you have a big group you might want to but for around 4 people you should be good.