Here are a few suggestions,,,
Cambalache has a new area of seating. It's a small little area outside the restaurant where the bar is. I think it would be perfect for single dining. I guess they added this because they were running out of room. Also the food is excellent. I would suggest the souffle potatoes and Arranchera beef. Sooo good. They also have a beautiful winelist.
Glazz has also opened up a great little "cafe" style place in La Isla Mall. They have their original restaurnat upstairs but now addedlike an express in the mall with chairs outside and a few inside. The food is similar to PF Changs and also has a sushi bar. I would suggest the Dragon roll. They have 3 different ones but the original Dragon does not have any raw stuff just cooked shrimp tempura and is sooo fabulous. I think it's enough for a meal! Greatdesserts too.
Chillies in La Isla has a bar area. Very good Boneless chicken wings, salads, fajhitas and more. American Mexican style.
Hanaichi if you like sushi., very fresh and I would never recommend anywhere else for sushi. You can eat at the sushi bar and they have fabulous rice (not raw) and great sashimi and rolls. Remember in Mexico they put creamcheese in them...gross? But be aware.
Tycoz for a quick and delicious sandwicxh. A few tables outside. In front of intercontenental Hotel and the owner is French and he makes one mean baguette!
The best time to eat in Cancun would be about 1:30 for lunch. Americans eat at around 12 or 1 p.m. and 6 p.m for dinner while Mexicans eat 2 or 3 p.m. lunch and 9 p.m. dinner