Step 1: Build the Flavorful Rice Base - Preheat your oven to 375 degrees and set out a 9 by 13 baking dish. In a mixing bowl stir together the broth, half the Japanese barbecue sauce, soy sauce, sesame oil, rice wine vinegar, and the first round of seasonings. Give it a good whisk so everything comes together. Pour that mixture into the baking dish, then stir in the rice, green onion whites, and carrots. This is where the magic starts because the rice is already soaking in flavor before it even hits the oven.
Step 2: Season and Glaze the Chicken - In a separate bowl toss the chicken thighs with the remaining garlic powder, onion powder, red pepper flakes, and pepper. Nestle the chicken right down into the rice mixture. Spoon and brush the remaining barbecue sauce over each thigh so they are nicely coated. I like to make sure every piece gets a glossy layer because that turns into a beautiful sticky glaze later.
Step 3: Bake Until Tender and Fluffy - Cover the baking dish tightly with foil. Really seal it well so the rice steams properly. Slide it into the oven and bake for 55 minutes. During that time the chicken gets tender while the rice drinks up all those savory juices. Your kitchen is going to smell incredible.
Step 4: Broil for a Caramelized Finish - Take off the foil and switch on the broiler for about 5 minutes. Keep an eye on it. You want the chicken edges bubbling and caramelized, not burned. This little finishing step is what gives the dish that glossy takeout style finish.
Step 5: Finish and Serve - Scatter sliced green onion tops over everything right before serving. Scoop the rice onto plates with a chicken thigh on top and make sure nobody misses a spoonful of that flavorful rice from the bottom of the pan.