In a small bowl, whisk together the tamari, rice vinegar, honey, grated ginger, minced garlic, and toasted sesame oil until well combined.
In a separate tiny bowl, stir the arrowroot powder and water together to create a smooth slurry and set it aside.
Season the cubed chicken breast evenly with the sea salt and black pepper.
Heat the avocado oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the chicken to the pan and sauté for 5-6 minutes, stirring occasionally, until golden brown and fully cooked through.
Remove the chicken from the pan and set it aside on a plate.
In the same pan, add the broccoli florets and sliced red bell pepper with a small splash of water, then cover with a lid for 2 minutes to steam.
Remove the lid and stir-fry the vegetables for another 2 minutes until they are crisp-tender and slightly charred.
Return the cooked chicken to the pan and pour the prepared sesame-ginger sauce over the mixture, tossing to coat everything evenly.
Stir in the arrowroot slurry and cook for 1 minute as the sauce thickens into a glossy glaze.
Serve the stir-fry immediately over the warm cooked brown rice and garnish with the freshly sliced green onions.