The fabled Hitchhiker's Guide to the Galaxy has the phrase "Don't Panic" inscribed on its cover. Lemon Grass would be wise to do the same with its menu. At most Vietnamese restaurants, first-time diners and aficionados alike fret as they skim the 100 or 150 or 200 choices. Where do I even start? What is the specialty of the house? At Lemon Grass the answers are, respectively, anywhere you want and pretty much everything: savory, herb-spiked pho; charbroiled meats doused with sweet, sneakily hot nuoc cham; bubbling hot pots; iced coffee strong enough to fuel you into next week; sparkling lemonade as crisp and refreshing as a spring evening. All you really need to know is the restaurant's name. Whatever you order will be as brightly flavored as that slender stalk.