We like Chevy's Fresh Mexican at the Crossroads of Lake Buena Vista (down the road from Disney Springs - you may want to drive instead of walk). it's not great, but not too bad. Otherwise, if you are looking for Tex-Mex, you won't find any at WDW. Some people say Pecos Bill's at the MK, but that is really, really bad now. If you want table service that is not Tex-Mex, you might check out Maya Grill for dinner at Coronado Springs Resort. It's not too bad.
My former CM son though Frontera was horrid.