Cho Sun Ok sits quietly and demurely on a windowless corner of North Center, looking as if it were a dying Asian restaurant. Nothing could be further from the truth. Inside, the small spot smokes with barbecue--Korean style. You can either do it yourself at your table or, if your table lacks a burner, have it done by the chef. Either way the tangy, marinated, thin slices of beef or pork are worth going out of your way for. They come with a multitude of condiments for creative noshing. Eating here is a true ethnic experience.