Preheat the oven to 375°F and lightly grease a 9x13 baking dish.
In a medium bowl, mix chicken broth, 1/2 cup Japanese BBQ sauce, soy sauce, sesame oil, rice wine vinegar, 1 tsp garlic powder, 1 tsp onion powder, 1 tsp red pepper flakes, and 1 tsp pepper until well combined.
Pour the mixture into the baking dish. Add rice, white parts of green onion, and carrots, then stir gently so everything is coated.
Season the chicken thighs with the remaining spices, place them on top of the rice, and drizzle with the remaining 1/2 cup BBQ sauce.
Cover tightly with foil and bake for 55 minutes.
Remove foil and broil for about 5 minutes until the chicken is caramelized and glossy. Top with green onions and serve warm.