Heat oil in a large skillet over medium heat. Add chicken, season with salt and pepper, and cook until golden and cooked through. Remove and set aside.
In the same skillet, add garlic (and ginger if using). Cook for 30 seconds until fragrant.
Pour in pineapple juice, soy sauce, brown sugar, and the cornstarch-water mix. Stir and let simmer until the sauce thickens slightly (2–3 minutes).
Add pineapple chunks and return the cooked chicken to the skillet. Stir to coat everything in the sauce. Simmer for 5 minutes.
Meanwhile, cook rice in a separate pot with water or broth until tender. (Or reheat leftover rice.)
Serve chicken and sauce over rice. Top with green onions, sesame seeds, chili flakes, or lime if you like.