In a small bowl, whisk together the coconut aminos, rice vinegar, tomato paste, honey, and toasted sesame oil until the sauce is smooth and well combined.
Dice the chicken breast into 1-inch bite-sized pieces and season evenly with sea salt and black pepper.
Heat the avocado 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 for 5-6 minutes, turning occasionally, until golden brown and cooked through; transfer to a plate.
In the same skillet, add the sliced red onion, red bell pepper, and green bell pepper, sautéing for 3-4 minutes until the vegetables are vibrant and crisp-tender.
Stir in the minced garlic, grated fresh ginger, and pineapple chunks, cooking for an additional 1 minute until the aromatics are fragrant.
Return the cooked chicken to the skillet and pour the prepared sweet and sour sauce over the top.
Toss everything together for 1-2 minutes until the sauce thickens slightly and coats every piece with a glossy sheen.
Serve the stir-fry immediately over the warm cooked brown rice for a complete, balanced meal.