Pat the chicken breast dry with a paper towel and cut into 1-inch uniform cubes.
In a small mixing bowl, whisk together the pineapple juice, coconut aminos, rice vinegar, tomato paste, minced ginger, and minced garlic until smooth.
Place the chicken cubes in a separate bowl and toss with arrowroot powder, sea salt, and black pepper until each piece is lightly and evenly coated.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the chicken to the skillet in a single layer and cook undisturbed for 3 minutes to develop a crust, then flip and cook for another 2-3 minutes until golden and crispy.
Remove the chicken from the skillet and set aside on a plate.
In the same skillet, add the sliced red bell peppers and broccoli florets, sautéing for 3 to 4 minutes until they are tender-crisp and bright.
Pour the prepared sauce into the skillet with the vegetables and bring to a light simmer for 1 minute until the glaze begins to thicken.
Return the crispy chicken to the skillet and toss quickly to coat every piece in the sweet and sour glaze.
Serve the hot stir-fry immediately over the portioned cooked brown rice.