We went at lunch time and they have a quite fairly priced lunch special set menu for 7000 KRW.
Lunch is available on weekdays from 11:30-2PM.
You can also order from the full menu if you want to try some of the more authentic flavors they serve. Judging by the tables around us, the softshell crab is definitely a go-to dish.
I think this is really my favorite Thai restaurants in Seoul, so definitely check it out and let me know what you think!
I forgot to take a menu of the full menu, but this is the lunch menu.
The owner is super nice and friendly and will be happy to tell you all about his travels, etc.
Sangsu Station - Take exit 1 and walk straight along the main road until you get to the first street...it's going to be a strange sort of curvy/crooked street. Take a right there. Stay to the right and keep following that street. You'll come to the second dead-end street and you'll see Mum Aroy straight ahead at the end of the dead end. It's on the second floor. If you get lost, just look up and look for the Thai flag.