Slice the onion thinly, julienne the carrot, and slice the green pepper into thin strips. Optionally microwave the carrot for 3 minutes at 600W to soften. In a small bowl, mix the sauce: sugar, soy sauce, sake, mirin, and rice vinegar.
Lay the pork on a plate and dust evenly with potato starch, tossing so every piece gets a light coating.
Heat sesame oil in a frying pan over medium-high heat. Add the garlic paste, then the pork. Stir-fry for 2–3 minutes until about 90% cooked through.
Add the carrot, onion, and pepper. Stir-fry for 2–3 minutes until the vegetables soften and any extra moisture cooks off.
Lower heat to medium-low. Pour in the premixed sauce and toss for 1–2 minutes until the sauce thickens slightly and clings to everything in a glossy glaze.
Plate immediately, sprinkle with white sesame seeds, and serve hot over steamed rice.