Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Dice the chicken breast into one-inch cubes and place them in a large mixing bowl along with the fresh broccoli florets.
In a small glass jar or bowl, whisk together the orange juice, tamari, honey, rice vinegar, sesame oil, arrowroot powder, minced garlic, and grated ginger until the starch is fully dissolved.
Pour exactly half of the prepared orange sauce over the chicken and broccoli, tossing thoroughly to ensure every piece is evenly coated.
Spread the chicken and broccoli in a single layer on the baking sheet and bake for 15 to 18 minutes until the chicken is cooked through and the broccoli is tender-crisp.
While the chicken is in the oven, pour the remaining sauce into a small skillet and simmer over medium heat for 3 minutes until it reduces into a thick, glossy glaze.
Divide the warm cooked brown rice into serving bowls, top with the baked chicken and broccoli, drizzle with the extra glaze, and finish with a sprinkle of sesame seeds.