Frontier specializes in low-frills, affordable New Mexican and American grub - there's often a long line of patrons, but it moves quickly. Service is fast and efficient. You order your food at the counter, wait for your number to appear on a flashing screen, and take it back to your table (basically, it's glorified cafeteria-style). There's no liquor license, but Frontier does serve a mean house-made lemonade as well as chai, cappuccino, and smoothies.
Best bets for breakfast are huevos rancheros and breakfast burritos, and definitely save room for one of the restaurant's trademark "sweet rolls" (basically Frontier's version of a cinnamon roll). For lunch and dinner, Frontier is known for its green-chile cheeseburger (the Fiesta burger, which you can have topped with red-chile, too, if you prefer), as well as carne adovada burritos, green-chile stew, beef tacos, and other New Mexico standards. There are better spots around town for authentic local food, but not many of them are this inexpensive or stay open this late. And as much as anything, dining at Frontier is about soaking up the quirky vibe and observing the often off-beat crowd.