In a bowl, mix soy sauce, pineapple juice, brown sugar, minced garlic, and black pepper to create the marinade.
Add chicken thighs to the marinade and refrigerate for at least 2 hours or overnight.
In a medium saucepan, combine jasmine rice, coconut milk, water, and salt. Bring to a boil, cover, reduce heat, and simmer for 18 minutes.
While the rice cooks, heat oil in a skillet over medium-high heat. Cook the marinated chicken until browned and fully cooked, about 6–8 minutes per side.
Add diced pineapple to the skillet and sauté briefly with the chicken.
Fluff the coconut rice and serve with the chicken. Garnish with green onions if desired.