Cook rice according to package directions. Steam or boil broccoli until desired tenderness is reached. Chop the scallions.
Meanwhile, prep your chicken and add it to a large ZipLoc bag along with the cornstarch. Toss until it's coated.
Add the sauce ingredients (garlic, brown sugar, ginger, mirin, soy sauce, water) to a small bowl and stir together.
Add the oil to a skillet, along with the chicken. Give it a stir and cook it over medium-high heat for a few minutes, stirring occasionally, until the chicken is no longer pink on the outside.
Pour the sauce into the skillet and reduce the heat to medium. Cook for a few more minutes until the chicken is cooked through and the sauce has thickened.
Divide the rice, broccoli, and chicken evenly among your four containers. Garnish with scallions. I suggest reheating these bowls in the microwave.