Pat chicken pieces thoroughly dry with paper towels. This helps them brown beautifully.

Heat cooking oil in a large skillet or wok over medium-high heat. Add chicken pieces in a single layer, making sure not to overcrowd the pan. Cook for 3-4 minutes per side, until deeply golden brown and cooked through. Remove chicken from the pan and set aside.

In the same pan, reduce heat to medium. Add soy sauce, brown sugar, rice vinegar, garlic powder, onion powder, red pepper flakes (if using), and 1/2 cup water. Bring the mixture to a simmer, stirring to dissolve the sugar.

Let the sauce simmer gently for 5-7 minutes, stirring occasionally, until it begins to thicken and reduce slightly. This crucial step concentrates the flavor and helps prevent a watery sauce later.

Add the pineapple chunks to the simmering sauce. Continue to simmer for another 3-4 minutes, allowing the pineapple to warm through and release some of its natural sweetness into the sauce without overcooking it.

In a small bowl, whisk together the cornstarch and 2 tablespoons of cold water until smooth to create a slurry. Pour the slurry into the simmering sauce, stirring constantly for 1-2 minutes until the sauce thickens to a glossy, desirable glaze consistency.

Return the cooked chicken pieces to the pan. Toss gently to coat the chicken and pineapple thoroughly with the rich, sticky glaze. Cook for another 1-2 minutes, allowing everything to heat through and meld.

Remove from heat. Garnish generously with fresh chopped parsley before serving.