In a medium bowl, whisk together soy sauce, brown sugar, ketchup, pineapple juice, minced garlic, grated ginger, sesame oil, and black pepper until the sugar fully dissolves.

Place the chicken thighs in a large resealable bag or shallow dish, then pour the marinade over them, ensuring each piece is fully coated. Refrigerate for at least 30 minutes.

Preheat your grill to medium-high heat (375°F to 450°F) and oil the grates lightly.

Remove chicken from the marinade and place on the grill. Grill for 6-7 minutes on each side until reaching an internal temperature of 165°F.

Heat oil in a skillet over medium heat, add mixed vegetables, and sauté for 5-7 minutes until tender yet vibrant.

To assemble, start with a base of rice, layer the sliced chicken on top, followed by the sautéed vegetables, and garnish with chopped green onions.