Preheat the oven to 425℉. Line a rimmed baking sheet with parchment paper, then lightly spray it with avocado oil spray (or brush with 1 tablespoon of avocado oil).
In a small bowl, whisk together the arrowroot starch, white rice flour, and sea salt.
Cut the chicken thighs into 1” cubes, then dredge in the flour mixture. Shake off any excess flour, and place the chicken pieces on one side of the baking sheet.
Slice the bell pepper and onions and spread them out on the other side of the baking sheet. Lightly spray the chicken and veggies with avocado oil spray (or brush with the remaining 2 tablespoons of avocado oil).
Bake for 20 minutes, then flip the chicken and pull the pan of veggies out of the oven. Bake the chicken for an additional 10 minutes until it's browned and crisp.
While the chicken and veggies are cooking, whisk together the pineapple juice, brown sugar, rice vinegar, ketchup, and soy sauce in a saucepan over medium heat. Bring to a boil. Whisk together 1 tablespoon arrowroot starch with 2 tablespoons of water in a small bowl, then add the mixture to the sauce and whisk to combine. Reduce the heat to low and remove the sauce from the heat once thickened.
Toss the chicken with the sweet and sour sauce, then garnish with white sesame seeds. Serve over white rice and enjoy!