Slice the chicken into thin, bite-sized strips and season with sea salt and black pepper.
Heat avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the chicken to the pan and sear until golden brown and cooked through, about 5-6 minutes.
Remove chicken from the pan and set aside; add the bell peppers, garlic, ginger, and chili to the same pan.
Sauté the vegetables for 2-3 minutes until the peppers are tender-crisp and the aromatics are fragrant.
Whisk together the tamari, fish sauce, and coconut sugar in a small bowl.
Return the chicken to the pan and pour the sauce over the mixture, tossing to coat evenly.
Turn off the heat and fold in the fresh Thai basil leaves until they are just wilted.