Seasons change, even in perennially temperate San Francisco. Restaurants may change seasonally too, with a dramatic monsoon debut followed by a dry spell of ordinariness. A gourmet destination may run hot, lukewarm, then cold, fluctuating with the seasons -- from autumn's bountiful harvest to winter's hearty fare; to fresh spring greens marching into summer's outdoor sizzle. Hung, the head chef, and Tessa Le, the manager of front operations, are the creative team behind Three Seasons, a hip Vietnamese hot spot that has flourished for almost four years in the trendster Marina District. Flying in the face of the Bay area's "mean and lean" seasonal downturn, they have opened two sister restaurants of the same name (in Palo Alto and Walnut Creek) to make it three in all. Three Seasons refers to the three seasons -- Fall, Spring and Summer -- in South Vietnam, and to the post-revolutionary film of the same name. -- Laurel Timms