Yes, “Asian fusion” is the culinary equivalent of the American wearing a beret in Paris; the guy from Riverside with a koi tattoo. Yet, most global cuisines are fused. And Jo Ann Plympton’s roast duck in black vinegar sauce with sake fruit is some delicious Asian food by an Anglo-Saxon. Duck skin crackles like hot martini ice. Her grilled Shanghai beef in Japanese mustard vinaigrette also makes us proud to be meat eaters. Try it all at Gang Kitchen, a 5,000-square-foot warehouse—austere in black, silver, and concrete—that’s in need of a couch or a woman’s touch. But the taste needs no help at all. 345 Sixth Avenue, downtown