Gangnam has to be the high-end place always in a bustle full of lovers and foreigners. As for being the center of a business district, it offers fairly high quality restaurants.
But to keep it light for the travellers here are some places that are pleasant and delicious.
Get off at Gangnam station, out through exit #6.
Walk straight up the street until you get to Giordano. You'll find a small entrance to 'Pepe viola'. It serves real nice Italian food as a buffet at lunch time and as a order-meal at dinner.
Walk further up until you find 'Keumgang shoes'. Across the alley on the second floor you can find 'Primo piatto'. It also is a bright, cozy Italian restaurant with real nice thin pizzas.
Not so much "Korean" but for those who may miss western food.