Saute the onion and pepper in canola oil until tender. Add pineapple chunks. Set aside.
Add the ingredients for the tempura batter in a bowl set over a second bowl of ice water. Whisk lightly to combine. Dredge the chicken breasts in the tempura batter and fry on both sides until golden and crispy. Drain on paper towels.
Add the duck sauce, ketchup, brown sugar and pineapple juice to a pot and bring to a boil. Simmer for a few minutes, until slightly thickened. Add the sauteed onion, pepper and pineapple to the sauce.
Place tempura fried schnitzel on serving dishes and spoon sauce over it. Garnish with sesame seeds.