Chef Michael Costa knows that if you ask diners if they'd like a lamb chop or crown roast, you may get some wary looks. Isn't lamb a bit expensive? And gamey?But offer them an Adana kebab - spiced ground lamb wrapped around a skewer and grilled to sizzling perfection - and you may have a new lamb fan."It's kind of a gateway drug," jokes Costa, chef at Zaytinya in Washington, D.C., part of Spanish-American chef Jose Andres' restaurant group.