Zen, which opened in May, actually stretches the concept quite a bit. In a phone interview, owner Raymond Ng says that the clientele, mainly young urban dwellers who are well acquainted with sushi, push for more than the basics. ‘‘We try to go toward contemporary fusion,’’ Ng says, pointing to such dishes as plum duck made with ‘‘real plums imported from Japan,’’ grilled ribeye and grilled rack of lamb, plus stone grill entrees. But Zen covers the bases nicely with De Guan, called De San, who had been at the famed Oishii, creating the sushi. The lineage shows. One evening, a special of bluefin toro (fatty tuna) with a spicy sauce looks very Oishii, its prime ingredients lavishly piled together into a delightful, if messy, dish. Unagi salad — the eel, avocado, and shredded daikon radish piled into a big martini glass and garnished with thin slivers of cucumber and dots of tobiko — is both delicious and fun. It’s easier to eat than the toro, since the container holds the ingredients together.