Pat the chicken breast dry with a paper towel and cut into 1-inch bite-sized chunks.
In a medium bowl, toss the chicken with arrowroot powder, sea salt, and black pepper until every piece is lightly coated.
Heat the sesame oil in a large non-stick skillet or wok over medium-high heat until shimmering.
Add the chicken to the skillet in a single layer and sear without moving for 3 minutes to develop a crust.
Flip the chicken and cook for another 3 minutes until golden brown and cooked through, then remove from the pan and set aside.
In the same skillet, add the sliced red bell pepper and snap peas, sautéing for 3-4 minutes until they are tender yet still vibrant.
Stir in the pineapple chunks, coconut aminos, rice vinegar, and honey, scraping up any browned bits from the bottom of the pan.
Return the chicken to the skillet and toss continuously for 1 minute until the sauce thickens into a glossy glaze that coats everything.
Place the warm cooked brown rice in a bowl and top with the sweet and sour chicken stir-fry.
Garnish with sesame seeds and thinly sliced green onions before serving immediately.