After eating at Matta's once, I felt that the ambiance and service were good, but the food was only ok. And vegetarians should avoid Matta's unless it's for the bar.
My vegetarian friend was with me and when we asked the host if he knew if the beans were vegetarian he seemed confused, then disappeared into the back for a few minutes. When he came back, he told us that everything was cooked with lard except the rice and a meat dish...so not a good place to go with a vegetarian.
On the positive side, we both thought margaritas were good. So go for the ambiance and drinks.