Tueng Chiang Mai (ถึงเจียงใหม่) is a real hidden gem, set in a leafy little courtyard in the maze of soi across Suthep road from Chiang Mai University. It's really only known about by students, as is attested by the doodles, proverbs and decalarations of love all over the tables made out of ancient sewing machines. The menu is cheap, delicious and includes a lot of dishes you don't see very often, like stir fried golden pumpkin and chayote shoots with chilis and minced pork, and all of it tastes home made. They also use duck eggs if you ask. Check the chalkboard if you can read Thai, because they sometimes have special seasonal dishes with cool stuff like wild mushrooms.
You probably won't have any room left after a meal at Tueng, but if you're still hungry you can stop by one of the gazillion stalls along Suthep road.