Pat the chicken breast dry with paper towels, cut into bite-sized pieces, and toss in a bowl with arrowroot powder, sea salt, and black pepper until evenly coated.
Heat half of the toasted sesame oil in a large non-stick skillet or wok over medium-high heat.
Add the chicken to the skillet in a single layer and sear for 3-4 minutes per side until golden brown and cooked through, then remove from the pan and set aside.
Add the remaining sesame oil to the same pan along with the broccoli florets and diced carrots, sautéing for 3-5 minutes until tender-crisp.
Stir in the minced garlic, grated ginger, and frozen peas, cooking for 1 minute until the aromatics are fragrant.
Add the cooked brown rice and tamari to the skillet, pressing the rice down with a spatula and letting it sit for 2 minutes to develop a slight crisp.
Return the cooked chicken to the pan and toss everything together with sliced green onions before serving warm.