Marinate the pork belly slices in the hoisin sauce, brown sugar, and soy sauce, for up to 24 hours.
Preheat the oven to 375 F. Line a baking sheet with tinfoil.
Set the pork belly slices on the baking sheet and cook for 30 minutes, turning halfway. The pork belly should be slightly caramelized and be a little squishy when poked. They will be hard and dry if overcooked, so keep an eye on them.
Remove from the oven and let rest for 10 minutes. Then slice into 1"x1" pieces.
Add the chopped cucumber, radish, and onions to a bowl. Season with salt.
To assemble, place a slice of pork belly on a cracker. Top with some of the salad, Sriracha mayo, and Togarashi seasoning.