In a small bowl, whisk together the soy sauce, brown sugar, ginger, garlic, and cornstarch until the cornstarch is fully dissolved.
Heat vegetable oil in a large wok or skillet over medium-high heat.
Add chicken cubes to the pan and sear until browned on all sides and cooked through, approximately 5 to 7 minutes.
Add the diced red bell pepper to the skillet and sauté for 3 minutes until slightly softened.
Incorporate the pineapple chunks and cook for an additional 2 minutes until the fruit is heated through and slightly caramelized.
Pour the sauce mixture into the skillet and stir constantly to ensure even coating.
Simmer the mixture for 2 minutes or until the sauce has thickened to a glossy glaze.
Divide the cooked jasmine rice into four serving bowls and top with the pineapple chicken mixture.
Garnish with sliced green onions and serve immediately.