Cut the chicken breast into uniform 1-inch cubes for even cooking.
In a small bowl, whisk together the tamari, honey, rice vinegar, minced fresh ginger, minced garlic, and red pepper flakes.
In a separate small ramekin, stir the arrowroot powder and water together to create a smooth slurry.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat.
Add the chicken cubes to the skillet and sauté until they are golden brown on all sides and cooked through.
Add the broccoli florets and sliced red bell pepper to the pan, sautéing for 3-4 minutes until the vegetables are tender-crisp.
Pour the tamari sauce mixture over the chicken and vegetables, tossing well to coat.
Stir in the arrowroot slurry and simmer for 1 minute until the sauce thickens into a glossy glaze.
Serve the stir-fry immediately over the warm brown rice, garnished with sliced green onions and sesame seeds.