Shreds of chicken drenched in fiery chiles; beef, roasted and then stewed, as rich as barbecue; chunks of pork in sweet red roasted-poblano chile sauce; sizzled strips of steak with roasted tomatoes; chunks of pork in zingy tomatillo sauce with potatoes... Confronting the ever-changing steam trays in the cafeteria line at El Burrito Mercado can make you swoon with possibilities--and there're always at least six hot and potent options. Announce your burrito intentions, and the workers behind the counter throw an oversize flour tortilla on the grill, dress the disk with silky refried beans, add fresh grated cheese, then ladle on generous quantities of your choice of meat. Now you've got a six-inch bundle of goodness, all yours and all for a mere $3.50 ($5.25 with more beans and rice on the side). Choose a beverage--Mexican Coke is popular, but a fresh fruit licuado made with blended watermelon or strawberries is great too. Pay (1999 brought a credit-card option), and tote your burrito down to the end of the counter for further doctoring: two kinds of salsa, chopped cilantro, jalapeño pickles, onions, fresh lime quarters. As you pierce the tender burrito with your fork, be sure to give a silent moment of praise for food with as much personality and verve as the bright piñatas floating above your head.