Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
In a small mixing bowl, whisk together the fresh orange juice, tamari, rice vinegar, honey, minced ginger, minced garlic, and arrowroot powder until smooth.
Place the cubed chicken breast and broccoli florets on the prepared baking sheet, drizzle with sesame oil, and season with sea salt and black pepper.
Pour half of the orange sauce mixture over the chicken and broccoli, tossing thoroughly to ensure every piece is well coated.
Spread the mixture into a single layer and bake for 15-18 minutes until the chicken is cooked through and the broccoli is tender-crisp.
While the chicken bakes, pour the remaining orange sauce into a small saucepan and simmer over medium heat for 3-5 minutes until it thickens into a glossy glaze.
Remove the tray from the oven, drizzle the thickened glaze over the chicken and broccoli, and garnish with sesame seeds and sliced green onions before serving.