Preheat the oven to 375°F (190°C) and lightly spray a 9×13-inch baking dish with cooking spray.
Make the teriyaki sauce: in a medium saucepan combine soy sauce, brown sugar, minced garlic, ground ginger, and red pepper flakes; bring to a boil over medium-high heat while whisking nearly constantly.
In a small bowl whisk together the cornstarch and 1/2 cup water until dissolved, then add this mixture to the boiling soy mixture; simmer and stir for 1–2 minutes until the sauce thickens, then remove from heat and set aside.
Assemble the baking dish: add the minute rice, canned pineapple with its juice, diced red bell pepper, and chicken broth to the prepared dish; stir gently to combine. If using, stir in chili garlic sauce to taste.
Arrange the chicken breasts evenly on top of the rice mixture.
Spoon a generous amount of the prepared teriyaki sauce onto each chicken piece, reserving any extra sauce separately (do not double-dip into the sauce with a utensil that touches raw chicken).
Cover the dish tightly with foil and bake for 30 minutes.
Remove the foil and bake uncovered for an additional 5–10 minutes, until the chicken is cooked through and the rice is tender.
Garnish evenly with sliced green onions and optional sesame seeds, then serve immediately with reserved teriyaki sauce if desired.