Pat the chicken breast dry with paper towels and cut into bite-sized pieces.
In a medium bowl, toss the chicken with arrowroot powder, sea salt, and black pepper until evenly coated.
Heat the avocado oil in a large skillet or wok over medium-high heat.
Add the chicken to the pan and sear until golden brown and cooked through, about 6-8 minutes, then remove and set aside.
Add the diced bell pepper, snap peas, and pineapple chunks to the same pan, sautéing for 3-4 minutes until the vegetables are tender-crisp.
In a small jar or bowl, whisk together the coconut aminos, rice vinegar, grated ginger, minced garlic, and toasted sesame oil.
Return the chicken to the skillet and pour the sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce thickens into a glossy glaze.
Serve the hot stir-fry over the cooked brown rice.