In a small bowl, whisk together the tamari, rice vinegar, honey, toasted sesame oil, minced ginger, minced garlic, red pepper flakes, and arrowroot powder until smooth.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the cubed chicken breast to the skillet and sear, stirring occasionally, until golden brown and cooked through, about 6 minutes.
Remove the chicken from the pan and set it aside on a plate.
Add the broccoli florets and sliced red bell pepper to the same skillet with a tablespoon of water, then cover for 2 minutes to steam-tenderize the vegetables.
Return the chicken to the pan and pour the prepared sauce over the mixture.
Stir constantly for 1-2 minutes until the sauce thickens into a glossy glaze that coats the chicken and vegetables evenly.
Serve the stir-fry immediately over a bed of warm brown rice and garnish with sesame seeds.