Dice the chicken breast into 1-inch cubes and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, apple cider vinegar, tomato paste, minced ginger, minced garlic, and arrowroot powder until smooth.
Heat the avocado oil in a large skillet or wok over medium-high heat.
Add the chicken to the skillet and sear until golden brown and cooked through, about 5-7 minutes, then remove from the pan and set aside.
In the same skillet, add the chopped bell peppers, red onion, and pineapple chunks, sautéing for 3-4 minutes until the vegetables are tender-crisp.
Return the chicken to the skillet and pour the sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce has thickened and coated the chicken and vegetables evenly.
In a separate pan, lightly steam or sauté the cauliflower rice for 3 minutes until tender.
Serve the sweet and sour chicken over the warm cauliflower rice and enjoy immediately.