Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into uniform 1-inch cubes and place them in a large mixing bowl.
In a small glass jar or bowl, whisk together the orange juice, orange zest, tamari, rice vinegar, honey, arrowroot powder, toasted sesame oil, minced garlic, and grated ginger until smooth.
Add the broccoli florets to the bowl with the chicken cubes and pour the orange sauce over the top, tossing well to ensure every piece is thoroughly coated.
Spread the chicken and broccoli mixture in a single layer onto the prepared baking sheet, ensuring there is space between the pieces for even roasting.
Lightly sprinkle the sea salt and black pepper over the tray.
Bake for 18 to 20 minutes, or until the chicken is cooked through and the sauce has reduced into a thick, sticky glaze.
Remove from the oven and garnish with sesame seeds before serving immediately.