Heat olive oil in a large skillet over medium heat.
Season the chicken cubes with salt and pepper, then cook in the skillet until browned and fully cooked. Remove and set aside.
In the same skillet, combine pineapple juice, soy sauce, and brown sugar. Bring to a simmer.
Mix cornstarch with a little water to create a slurry, then add to the skillet. Stir until the sauce thickens.
Add the cooked chicken and pineapple chunks to the skillet. Toss to coat evenly in the sauce.
Simmer for 2-3 minutes until everything is heated through.
Serve over steamed rice and garnish with green onions and sesame seeds, if desired.