In a small bowl, whisk together the coconut aminos, rice vinegar, tomato paste, and arrowroot powder until smooth to create the sauce.
Cut the chicken breast into bite-sized cubes and season with sea salt and black pepper.
Heat the avocado oil in a large skillet or wok over medium-high heat.
Add the chicken to the skillet and cook until golden brown and cooked through, about 5-7 minutes, then remove and set aside.
In the same skillet, add the chopped bell pepper and red onion, sautéing for 3-4 minutes until the vegetables are tender-crisp.
Add the pineapple chunks and the cooked chicken back into the skillet.
Pour the sauce over the mixture and stir constantly for 1-2 minutes until the sauce thickens and glazes the chicken and vegetables.
In a separate small pan, lightly sauté the cauliflower rice for 3 minutes until heated through and fluffy.
Serve the sweet and sour chicken over the cauliflower rice and garnish with sesame seeds.