First problem: Cooking the pork ahead of time seared the meat. You're not going to get anything other than cornstarch to stick to meat that's already been seared.
Second problem: The sugar syrup that made the sesame seeds stick to the cashews is also disrupting the ability of the cashews to stick to the meat. I'd try just using a mixture of toasted sesame and cashew, ground fine in the blender.
Best bet is to egg wash, then nuts, just like if you were doing it with a regular seasoned flour mixture.