If you're looking for a relaxed meal Old Chicago is probably the best place in the Boise Towne Square area. They primarily offer Chicago-style (thick crust) pizza. But they also offer a range of burgers and sandwiches and pasta as well. What pleases me the most, though, are the friendly servers. No matter how crowded it gets (and it can get full during lunch and dinner hours over the weekend, though the wait isn't long), the wait-staff still manages to be attentive and friendly. The atmosphere is casual and adults will definitely want to sign up for the Beer Tour and sample all 110 different beers available.
For basic casual "American" food, Old Chicago BTS is awesome.