Heat the oven to 375°F and lightly grease a 9-by-13-inch baking dish. If the chicken breasts are very thick, pound them to an even thickness so they cook at the same rate.

Whisk the pineapple juice, low-sodium soy sauce, brown sugar, ketchup, minced garlic, and ginger in a bowl until the sugar begins to dissolve. For optional marinating, reserve some sauce before adding the chicken, then refrigerate the chicken in the remaining sauce for 30 minutes to 8 hours.

Place the chicken in the prepared baking dish and pour the sauce over it. Arrange the drained pineapple, sliced red bell pepper, and sliced onion around the chicken.

Cover the dish tightly with foil and bake for about 20 minutes. Remove the foil and continue baking for 10–20 minutes, checking the thickest part of the chicken with an instant-read thermometer.

Continue cooking until the chicken reaches 165°F internally and the pineapple and vegetables are tender. If the chicken finishes before the sauce has reduced, remove the chicken and let it rest while you thicken the liquid separately.

For a thicker glaze, transfer the cooking liquid to a saucepan and simmer it for several minutes, or whisk in the cornstarch slurry and cook until thickened. Spoon or brush the finished glaze over the chicken, making sure any liquid that touched raw chicken has been thoroughly boiled.

Let the chicken rest for 5 minutes before slicing or serving. Finish with green onions and sesame seeds, then bring the baking dish to the table with your favorite rice and vegetables.