In a small saucepan, pour the soy sauce, sake and mirin.
Boil until reduced by half.
Set aside.
Stuff and roll the pork
Lay a pork cutlet flat and sprinkle with salt and pepper.
Arrange strips of bell pepper, carrot and asparagus on one side.
Roll as tightly as you can and secure with wooden toothpicks.
Repeat until all six pork cutlets have been filled and rolled.
Dredge the pork rolls in flour; shake off the excess.
Cook the pork
Heat enough cooking oil to coat the bottom of a frying pan.
Fry the pork rolls, rolling them in hot oil for even browning. If the pork cutlets are thin enough, the pork rolls should be cooked through in five to seven minutes.
Pour the teriyaki sauce into the pan. Swirl the pan to coat every inch of the pork rolls. Continue cooking until the meat has absorbed the sauce.
Scoop out the stuffed and rolled pork loin with teriyaki sauce.
When cool enough to handle, remove the wooden toothpicks and slice.
Serve the stuffed and rolled pork loin with bread, rice or salad.