Slice the chicken breast into thin, even strips and set aside.
In a small bowl, whisk together the tamari, minced ginger, minced garlic, and red pepper flakes to create the stir-fry sauce.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the chicken strips to the skillet and sear until golden brown and cooked through, about 5-6 minutes.
Remove the chicken from the pan and set it aside on a plate.
In the same pan, add the broccoli, sliced bell peppers, and snap peas, sautéing for 3-4 minutes until they are bright and tender-crisp.
Return the chicken to the pan and pour the tamari sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce thickens slightly and coats all the ingredients.
Remove from heat, drizzle with toasted sesame oil, and garnish with sesame seeds before serving.