In a medium bowl, combine the cut chicken pieces with 1 tablespoon of soy sauce, 1 teaspoon of cornstarch, ginger powder, and a pinch of black pepper. Toss well to ensure the chicken is evenly coated. Set aside to marinate for 10-15 minutes while you prepare the other ingredients.

In a separate medium bowl, whisk together the pineapple juice, 1/4 cup low-sodium soy sauce, rice vinegar, brown sugar, 1 tablespoon of cornstarch, minced garlic, grated fresh ginger, and red pepper flakes (if using). Whisk until the cornstarch and brown sugar are fully dissolved. Set aside.

Heat 1 tablespoon of olive oil (or sesame oil) in a large skillet or wok over medium-high heat. Once hot, add the marinated chicken pieces in a single layer. You may need to cook the chicken in two batches to avoid overcrowding, which can steam the chicken instead of searing it. Cook for 4-6 minutes, flipping occasionally, until the chicken is golden brown and cooked through. Remove the cooked chicken from the skillet and set it aside on a plate.

Add the remaining 1 tablespoon of olive oil to the same skillet. Add the diced red bell pepper, green bell pepper, and thinly sliced red onion. Stir-fry for 3-5 minutes, stirring frequently, until the vegetables are tender-crisp.

Return the cooked chicken to the skillet with the sautéed vegetables. Give the pineapple sauce a quick re-whisk to ensure the cornstarch hasn't settled, then pour it over the chicken and vegetables in the skillet. Bring the mixture to a simmer, stirring constantly, and cook for 2-3 minutes. The sauce will thicken and beautifully coat all the ingredients.

Gently fold in the pineapple chunks and cook for another minute, just long enough to warm the pineapple through.

Remove the skillet from the heat. Garnish generously with fresh chopped cilantro or sliced green onions. Serve your Sticky Pineapple Chicken Stir-Fry immediately over steamed white rice or your favorite noodles.