In a small bowl, whisk together the tamari, fish sauce, and coconut sugar until the sugar is dissolved.
Mince the garlic and thinly slice the Thai chilies, keeping the seeds if you prefer extra heat.
Heat the avocado oil in a wok or large skillet over high heat until it begins to shimmer.
Add the garlic and chilies to the pan, stir-frying for about 30 seconds until they release their aroma.
Add the thinly sliced chicken breast to the wok and cook, stirring frequently, until the chicken is browned and nearly cooked through.
Toss in the sliced bell peppers and trimmed green beans, continuing to stir-fry for 2 to 3 minutes until the vegetables are tender-crisp.
Pour the prepared sauce over the chicken and vegetables, tossing quickly to coat everything evenly.
Remove the pan from the heat and immediately fold in the fresh Thai basil leaves until they are just wilted.
Serve the stir-fry immediately over the portioned warm jasmine rice.