The yellow truck may not always be operational, but if you find Hallava Falafel with its service window open, step up and order a falafel sandwich. Packed into a fat pita with a piquant tzatziki dressing, tender shredded beets, salted cucumbers, lettuce, and a pickle spear, the fried chickpea rounds are in very good company. (The truck owner, however, may be brusque; ignore that.) Messy, well-balanced, and filling, this not-so-new portable meal is one of the tastiest you'll find.?Adriana Grant 5825 Airport Way S., 307-4769, myspace.com/hallava.