Prepare the Teriyaki Marinade: In a medium bowl, whisk together the low-sodium soy sauce, mirin, brown sugar, sesame oil, minced garlic, and grated ginger until the brown sugar is mostly dissolved. This will be the marinade for your chicken.
Combine with Chicken: Place your bite-sized chicken pieces into a large freezer-safe zip-top bag or a freezer-safe container. Pour the prepared teriyaki marinade over the chicken. Press as much air out of the bag as possible and seal it tightly. Squish the contents around to ensure all the chicken is evenly coated.
Label and Freeze: Clearly label the bag with the name of the meal ('Teriyaki Chicken') and the date. It's also helpful to include brief cooking instructions. Lay the bag flat in your freezer. This helps it freeze quickly and makes for easier storage.
Thaw the Meal: When you're ready to cook, it's best to thaw the frozen teriyaki chicken before cooking for the most even results. The safest method is to transfer the bag from the freezer to the refrigerator and let it thaw overnight (for at least 8-12 hours).
Cook the Chicken: Heat a large skillet or wok over medium-high heat with a splash of oil. Add the entire contents of the bag (chicken and marinade) to the skillet. Cook for 10-15 minutes, stirring occasionally, until the chicken is cooked through and the sauce has started to thicken. The internal temperature of the chicken should reach 165°F.
Thicken Sauce and Serve: While the chicken cooks, mix the 1 tablespoon of cornstarch with 2 tablespoons of water in a small bowl to create a slurry. Once the chicken is cooked, pour the slurry into the skillet and stir continuously for 1-2 minutes until the sauce thickens and becomes glossy. Serve your Freezer Meal Teriyaki Chicken hot over rice, garnished with sesame seeds and green onions.