By Paul Reidinger

paulr@sfbg.com

Over the years there have been a number of restaurants in San Francisco whose menus have featured regional, as opposed to national, dishes: Carta, 42°, Le Trou, and Square One spring immediately to mind, though all have departed. The catch, or proviso, typically has been that the regions are Mediterranean regions. Restaurants that serve the foods of Asia, by contrast, have often been linked to one nation or another: Thailand, China, Vietnam, India, Iraq. The exceptions – Straits Café, Malacca – have tended to have a Singapore connection, Singapore being one of the world's great international cities, a trading post for influences British, Portuguese, Chinese, subcontinental, and southeast Asian.

Mekong, as the name suggests, serves the foods of the Mekong River, one of the great streams of Asia and the world. The Mekong rises in the mountains of northwest China, flows between Myanmar and Laos and on through the Laotian capital, Vientiane, then becomes a long border between Laos and Thailand, and cuts through Cambodia before forming its delta in southern Vietnam and emptying into the South China Sea south of Saigon. On its 4,000-plus-mile journey (its exact length is uncertain, according to Wikipedia, because it rises in difficult terrain), it touches a host of culinary traditions, and while Mekong-the-restaurant's menu tilts decidedly in the direction of Thai, it also includes dishes from Tibet and Cambodia and features an entire section of "Mekong River seafood" (!) preparations, among them whole fish. And – the kicker – the restaurant claims to offer the widest variety of "Thai vegan" dishes in the city.

Quite a bit of the vegan stuff will be familiar to anyone who's ever eaten in a Thai restaurant – and around here that would include just about everybody, I would think. Mekong turns out a fine green-papaya salad ($5.95), with the fruit shredded into linguinelike threads and tossed with plenty of lime juice (to raise the pucker factor), crushed peanuts, lengths of forest-green Chinese long beans, and one's preferred level of chili heat. We opted for medium but nonetheless detected a slight smoky haze gathering about our heads as we ate; caution here is recommended. Spring rolls ($5.95) too are agreeable, though their innards – silver noodles, mushrooms, cabbage, carrot, scallion, and cilantro – are on the meek side, and salvation must be found in the thickened, sweet-salty sauce presented on the side of the platter.

Another good sauce, this one of peanut, appears with curry puffs ($5.95), half-moon-shaped pockets of rice paper filled with minced chicken, sweet potato, onion, carrot, and curry powder and then deep-fried. We did not find the deep-frying to be an occasion for joy, exactly (since the spring rolls were also deep-fried), but the curried sweet potato, velvety and rich, gave the puffs a striking character. It was as if they'd been stuffed with a thickened butternut squash soup.

Whole fish tend to be spectacular when plated, and Mekong's grilled rainbow trout ($8.50) is no exception. The downside – the price, we might say, of the spectacle – is that one generally must navigate around bones, a burden lightened in this instance by Mekong's lively marinade (of garlic, lemongrass, basil, cilantro, scallions, and onion) and a fine supporting cast of braised bok choy and crispy bits of ginger. The trout itself is flaky and white, like cod.

There are plenty of easier dishes to eat, among them a deeply satisfactory beef-basil stir-fry ($6.50), with plenty of garlic and julienne red bell pepper, and a simple but astonishingly tasty barbecue chicken ($7.50) – boneless strips of leg meat marinated in "Thai herbs and spices," grilled to a delicate golden char, and served with a ramekin of "special sauce" that struck us as being a relative of ponzu and nuoc mam, some blend of fish sauce and citrus or perhaps mild rice vinegar. Also user-friendly were the prawns with peanut sauce ($8.50); the crustaceans had been peeled for ease of eating and were slathered in a moderately fiery peanut sauce. Underneath: bean sprouts masquerading as pasta, commingled with carrot rectangles whose edges had been serrated.

Soups, naturally, are excellent. Although I have never had a bad tom kha gai – the signature Thai soup of coconut milk, lemongrass, galangal, cilantro, and Kaffir lime leaves – Mekong's version ($6.50) seemed to be particularly fresh, as if it had been given a good squeezing of lime before being brought to the table. For heft there was a wealth of mushroom slices and chunks of boneless chicken (with shrimp available for a small surcharge). And Khmer silver noodle soup ($6.50) could hardly have a lovelier name or a more straightforward recipe for success: chicken broth with nappa cabbage and spinach, chunks of boneless chicken, a kelp bed of translucent rice noodles, and flavor assistance from scallions, cilantro, and fried garlic. It was the sort of nourishing, penetrating, irresistible soup you would be glad to have brought to you on some dreary winter day when you had the sniffles.

Inside, Mekong isn't much to look at, apart from the large, mezzaluna shaped fans that serve as table dividers. There is free WiFi access (though we saw no one taking advantage of it) and, outside, the full chaotic glory of the Tenderloin, a region of Thai and Vietnamese restaurants and clumps of young men yakking at corners – streams of other consciousnesses bubbling at the edges of one's own.

Mekong Restaurant Daily, 11-1 a.m. 791 O'Farrell, SF (415) 928-2772 No alcohol MC/V Not noisy Wheelchair accessible