Tusker House is my favorite for both breakfast and lunch. Huge portions, terrific quality, and an dair conditioned dining room all make it perfect on a hot day.
Flame Tree BBQ comes in second. The food there is also excellent, and the menu is completely different from Tusker House, but the dining area is outdoor.
You could also try the Rainforest Cafe just outside the park entrance. In my experience, this one is far superior to the Rainforest at Downtown Disney, and is seldom crowded.