Sherri:
The short answer to your question of whether there is another quick-service dining restaurant at Epcot during Cantina de San Angel's renovation is 'no.' (Unless you count getting some of the flan from the dessert case at Sunshine Seasons over in Future World.)
However, Mexico's new
La Cava del Tequila offers tapas (appetizers) to accompany all of the tequilas they serve. And one could argue you could certainly make a meal out of these. But let me caution you, "quick" may not be the term to use for this establishment in the Mexico pavilion because you can't make ADRs for it. You'll find a more comprehensive synopsis of the bar on the Disney Food Blog (just google it + La Cava del Tequila). Although I haven't been to it yet, I've been living vicariously through the tastings of AJ at the Disney Food Blog and fellow Moms Panelists Jodi, Margaret, and Tanya who celebrated Margaret's birthday there in June. They gave it a thumbs-up.
Before I sign off, you mention that you are on the Deluxe Plan. Usually that plan offers plenty of food--so much that dining out of pocket isn't warranted. If La Cava doesn't look like your cup of tea, have you considered using one of your plan's ADRs at San Angel Inn? Although it's not the place to go for Mexican fare ala burritos and tacos, the theming is tranquil if not down-right romantic and makes up for the ho-hum menu selections.
Wishing you a magical dining experience!
Whitney