Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
In a small bowl, whisk together the fresh orange juice, tamari, honey, sesame oil, grated fresh ginger, minced garlic, and cornstarch until the mixture is smooth and well combined.
Place the cubed chicken breast and broccoli florets into a large mixing bowl and season them with sea salt, black pepper, and red pepper flakes.
Pour half of the prepared orange glaze over the chicken and broccoli, tossing everything together until each piece is thoroughly coated.
Spread the chicken and broccoli in a single layer on the prepared baking sheet, ensuring they aren't overcrowded to allow for even roasting.
Bake for 15 to 18 minutes, or until the chicken is cooked through and the broccoli is tender with slightly charred edges.
Remove from the oven and drizzle the remaining orange glaze over the hot chicken and broccoli to intensify the flavor.
Serve the orange chicken and broccoli immediately over a bed of warm cooked brown rice.