The only Portuguese restaurant I've been to in Seoul, Taverna de Portugal (터버나드포르투갈), has became one of my favorite places to go to, especially when I'm craving Nando's Chicken (which I haven't eaten in ages btw). Granted, the taste is not is exactly the same (according to a friend of mine who knows for sure what it tastes like), but their Grilled Piri Piri Chicken (피리피리치킨) is super delicious and full of flavors and it's good enough to fulfill my cravings :p
Located in a small alley in Sangsu (상수), the restaurant is owned by a friendly husband and wife duo. The place is not too big and it gets pretty busy during dinner time, especially on weekends. I usually ordered the Piri Piri Chicken Combo Menu 1 (피리피리 치킨 콤보메뉴 1), which consists of one whole grilled chicken, rice, sausage, bacon, salad, potatoes and home-made chips. It's good for 2 people and if you think that you need more food, they also have other selections on the menu.
They are currently having a summer special menu: Piri Piri Grill Fish Combo—oven grilled whole fish with piri piri sauce (minimum 1 day pre-order is required). Check out their facebook page for more info.
Tips: Come during lunch time if you want to avoid the crowd.