Earlier this year Highland Park’s Once Upon a Bagel bakery and deli—source of the quintessential egg bagel, the chocolate-chip bagel ball, and a mish-mosh soup that’ll cure just about anything—ventured into something a whole lot less kosher. A mile or so to the north, in the same Highwood strip mall that houses its hot dog outpost, the Mean Weiner, Once Upon opened a seafood diner, Lucky Fish Deli. The two small dining rooms, furnished with wood and Formica kitchen tables and comfy vinyl chairs, are separated from an open kitchen by a glass case that shows off scrupulously fresh denizens of the deep blue: oysters, lobster, shrimp, mussels, and clams, along with less trayf offerings like delicate lake perch (by the pound or half pound), which you can order fried, though I recommend it lightly blackened from the grill; either way, get it with the warm kettle chips or crunchy broccoli slaw....