Perhaps there's no food staple that points to the core of the Mexican psyche like the tortilla. Strikingly simple and rustic, the flat discs of corn, water and limewater inspired the late Chicano singer Lalo Guerrero's pouty "There's No Tortillas." Unfortunately, bad corn tortillas — thin, dry pucks from the grocery store — recall cardboard more than the spongy, doughy pillows of Mexican cuisine. But in the last 10 years, L.A. has awakened to a fresh wave of Latin American immigrants, which has revitalized the food scene. On a stretch of Pico Boulevard in Mid-City a small Oaxacan tortillaria, Tortilleria Expresion Oaxaquena took root four years ago. It offers a Qaxacan speciality: steamy packages of 12-inch tortillas that are about a millimeter thick and always soft and moist. They make them from corn, on the spot, throughout the day (and often late into the night), and they keep them in a cooler (a warmer, really) that was once a refrigerator. The prices usually beat the dull stuff at Ralphs. A dozen of the big tortillas costs $2. 3301 W. Pico Blvd. (323) 766-0575.