Slice pineapple in half, leaving the stem intact. Slice fruit around the perimeter, angling knife toward the middle. Scoop chunks out with a spoon and reserve 1 Tbsp. pineapple juice for sauce. Chop removed pineapple into smaller pieces for garnish or to snack on later. In a small bowl, whisk together soy sauce, brown sugar, pineapple juice, garlic, ginger, and sesame oil. Season chicken with salt. In a large skillet over medium-high heat, heat vegetable oil. Add chicken in an even layer and cook until golden brown. Pour sauce over chicken and bring mixture to a simmer. Whisk together cornstarch and water, then stir into sauce. Simmer until sauce is thickened and chicken is cooked through. Divide rice and chicken between bowls. Optional: Garnish with pineapple, sesame seeds, or green onions.