Prepare the Rice: Rinse the rice under cold water until the water runs clear. In a medium saucepan, combine the rice, water, and salt. Bring to a boil, then reduce heat to low, cover, and simmer for 18 minutes, or until all the water is absorbed. Fluff with a fork and set aside.

Marinate the Chicken: In a medium bowl, combine the chicken cubes with soy sauce, rice vinegar, sesame oil, and cornstarch. Toss to coat evenly and let marinate for at least 15 minutes (or up to 1 hour in the refrigerator).

Make the Sauce: In a separate bowl, whisk together the pineapple juice, brown sugar, soy sauce, ketchup, rice vinegar, cornstarch, ginger, and garlic. Set aside.

Cook the Chicken: Heat olive oil in a large skillet or wok over medium-high heat. Add the marinated chicken and cook, stirring occasionally, until browned and cooked through (about 6-8 minutes).

Combine and Simmer: Pour the sauce over the cooked chicken. Add the pineapple chunks. Bring to a simmer and cook, stirring constantly, until the sauce has thickened (about 2-3 minutes).

Serve: Serve the Pineapple Chicken over the cooked rice. Garnish with chopped green onions, sesame seeds, and red pepper flakes, if desired.