Tusker House at AK has some great veggie dishes on the buffet, and it might be easier to get to than Boma, depending on your situation.
Check out menus at allears.net. Most table service restaurants have at least one veggie option, and most are very willing to make changes if there is something in the dish that isn't to your liking.
Most counter service restaurants have a veg option, too, but, again, it is usually just one and it isn't as easy for CS places to modify. I will second the Lighthouse Sandwich at Columbia Harbour House! Check out options in Morocco and Sunshine Seasons in Epcot, too.