Sleepy Hollow and Gaston's are our "go to" easy breakfasts in MK. For the record, Gaston's will also sell you a pork shank at breakfast if you want to balance out the sweet from the cinnamon roll (and I did). Be Our Guest is also technically a counter service option at MK if you want something slightly more proper.
Within the last year, I have discovered the Joffrey's carts at AK and HS as a source of an excellent apple fritter (for me) and giant frosted donuts (to my kids' delight). The other AK kiosk I can think of is Kusafari Bakery back in Africa, which has a nice breakfast wrap in addition to the muffins, cinn rolls, etc.
And I'll pile on to the other recommendations of the France bakery in Epcot. You almost have the place to yourself at breakfast, as people either still don't realize it's open or just don't want to walk all the way back there if nothing else in WS is really open until 11:00.