I echo recommendations for Jiko. Not sure of your party and/or if on dining plan (if it returns) - it is a signature restaurant. Not only is the restaurant itself outstanding but I think the whole resort is truly beautiful and unique and it's easy to "make a night out of it" (Jiko is only open for dinner) exploring the resort, looking at exhibits in the lobby, talking to cultural representatives, viewing animals on the savanna (they even have night vision goggles after dark), shopping in their store etc.
I've not been yet but Topolino's is next on my list. I've heard great things about both the character breakfast and dinner.
Also really enjoy Flying Fish, bluezoo at the Dolphin (next to Boardwalk), California Grill. All of these are dinner only (though California Grill offers brunch on Sunday - or at least they did...)
Again, depending on your party, a "do-it-yourself" tour of the monorail resorts stopping in various lounges for a bite and then exploring each resort a bit can be really fun too.
Lastly, not resorts but tons of great options at Disney Springs for a non-parks day. My favorites are Wine Bar George, Boathouse, and Raglan Road.
