I first found this on Nok hub world, the second quest Green Loontern takes you on is to defeat 20 bad guys in an underground area lines with cells. Look in one of the top cells to find some odd potato head looking thing and kill it.
There is also one on Zamaron on top a mountain/hill close to where Loontern gives you his third quest.
On Ysmault there is a fire you need to put out to obtain Heatwave's character stud. On the side of that building is a large crack that can be broken open. Inside is another doughnut.