In a saucepan, whisk together the pineapple juice, sugar, rice vinegar, ketchup, and soy sauce.
Heat over medium low, stirring occasionally, until the mixture comes to a gentle simmer.
In a small bowl, mix the cornstarch and water until smooth, then pour it into the sauce.
Reduce heat to low and cook, stirring constantly until thickened, about 1 minute.
Remove from heat and set aside.
In a bowl, toss the chicken with the cornstarch, seasoning salt, paprika, garlic powder, and pepper until evenly coated.
Heat 2 tablespoons of the avocado oil in a large pan over medium heat.
Add the red pepper and onion and cook for about 8 minutes, until softened and lightly browned.
Remove the vegetables from the pan and set aside.
Add the remaining 2 tablespoons of oil to the pan, then add the chicken.
Cook for about 6 minutes, stirring occasionally, until the chicken is golden and fully cooked through.
Return the vegetables to the pan, pour in the prepared sauce, and toss everything together.
Cook for 1–2 minutes.
Serve over white rice and finish with green onions.
