Rinse the rice under cold water until the starch runs clear, then combine with 3.5 cups of water in a heavy-bottomed pot, bring to a boil, and simmer covered for 18 minutes.

Whisk the soy sauce, brown sugar, mirin, minced ginger, and minced garlic in a small bowl until the sugar solids are largely suspended.

Heat the vegetable oil in a large non-stick skillet or carbon steel wok over medium-high heat until shimmering.

Add the chicken cubes to the skillet in a single layer and sear for 8 to 10 minutes, turning occasionally until an internal temperature of 165°F (74°C) is reached.

Reduce the heat to medium and pour the soy sauce mixture over the chicken, allowing it to reach a gentle simmer for 2 minutes.

Integrate the cornstarch slurry into the simmering sauce and stir constantly for 60 seconds until the glaze reaches a nappe consistency.

Portion the steamed rice into bowls, top with the glazed chicken, and garnish with sliced green onions for service.