Preheat your oven to 375°F and spray a 9×13-inch baking dish with cooking spray. This ensures that nothing sticks and makes for easy cleanup later.
In a medium saucepan, add the soy sauce, brown sugar, garlic, ginger, and red pepper flakes. Bring this mixture to a boil over medium-high heat, whisking nearly constantly to dissolve the sugar and meld the flavors.
In a small bowl, combine the corn starch and water, stirring to dissolve. This slurry will help thicken your teriyaki sauce.
Pour the corn starch mixture into the boiling soy sauce mixture, stirring continuously. Bring everything to a low simmer and cook for 1 to 2 minutes, or until the sauce thickens to your desired consistency. Once that's done, set the sauce aside.
In the prepared baking dish, add the rice, the pineapple and its juice, red pepper, and chicken broth. If you like a kick of heat, you can also add the optional chili garlic sauce. Stir gently to combine all the ingredients.
Lay the chicken breasts evenly on top of the rice mixture. Make sure they’re spread out and not overlapping, so they cook evenly.
Dollop a generous amount of the prepared teriyaki sauce over each piece of chicken. Avoid double-dipping to keep the sauce safe for later use. Reserve any extra teriyaki sauce for serving.
Cover the baking dish tightly with foil and place it in the oven. Bake it covered for 30 minutes. This allows the chicken to steam and cook through.
After 30 minutes, remove the foil and bake for an additional 5 to 10 minutes, or until both the chicken and rice are cooked through. You should see a nice golden color on the top of the chicken.
Once done, sprinkle with green onions and optional sesame seeds for garnish. Serve immediately with the reserved teriyaki sauce if desired.
