If you're looking for authentic Mexican cuisine and you live in Westchester you must stop at Mr. Taco on North Avenue in New Rochelle.
Their guacamole is just amazing. They even import their soda from Mexico.
Having lunch there on Sunday we saw something that blew both of our minds. A family arrived with two girls who had to be 4-5 years old.
Each was drinking a Red Bull. While the small can proportionally looked more normal than a can of soda, I can't imagine what effect the caffeine would have on them.