Outside dining in Waltham, Watertown, Newton?
I'd personally pass on Margarita's and go to Taqueria Mexico. Just beer and wine if you are drinking but the food is much better.
In between Margarita's and TM is Biaggio. They have a roof deck which is nice. Last year I had some spotty service out there, but it may have improved. Also, I believe they only give you an app menu on the patio, but I asked our waitress last time and she said they would serve us dinner. You may want to ask first.
Across from Calvary cemetery is Paisano's. I had a terrible dinner there 2 yrs ago, but they had just opened. They seem to draw a decent crowd lately, so it may have improved.
Solea on Moody St. isn't outdoors, but you might be able to snag a table by the open windows.
In Newton Center, Sol Azteca and Union Street have outdoor patios. Sol Azteca serves Mexican and Spanish food (same as the one in Brookline). Union Street is a step up from basic pub grub and usually has a nice selection of beers on tap.
A couple exist in Watertown, both among the better restaurants in Watertown, though both somewhat erratic in my experience:
La Casa De Pedro (Venezuelan & other S. American)
La Casa De Pedro Alarcon
343 Arsenal St, Watertown, MA 02472
47 Main St, Watertown, MA 02472