Preheat convection oven to 375°F (190°C). Grease a 9x13-inch ceramic baking dish.
In a small saucepan over medium heat, whisk together soy sauce, water, brown sugar, ginger, and garlic.
In a separate small vessel, mix cornstarch with 1 tablespoon of cold water to form a slurry; whisk into the saucepan.
Bring sauce to a simmer for 3 minutes or until viscosity increases to coat the back of a spoon; remove from heat.
In a large mixing bowl, combine the diced raw chicken, cooked rice, frozen vegetables, and broccoli florets.
Pour the thickened teriyaki sauce over the chicken and rice mixture, folding gently until all surfaces are evenly coated.
Distribute the mixture evenly into the prepared baking dish.
Cover the dish tightly with aluminum foil to retain moisture and bake for 30 minutes.
Remove foil and continue baking for 15 minutes until the chicken reaches an internal temperature of 165°F (74°C) and the sauce is bubbling.
Allow the casserole to rest for 5 minutes, then garnish with sesame seeds prior to service.