Now thinly slice 2 lb of boneless skinless chicken thighs into strips. Place the sliced chicken in a large bowl and 1/3 cup cornstarch.
Heat 1/3 cup corn oil in a large wok over high heat. Cook the chicken in batches to ensure a crispy texture on the exterior. You don’t want to overcrowd the pan.
Once all of your chicken is cooked, transfer it to a separate bowl.
Then slice up one large yellow onion and mince 1 garlic clove and stir it in the same wok. Add oil as needed.
After the onion is cooked through, add the chicken back in. 
Heat 2 Tablespoons of corn oil in a small saucepan over medium-high heat. Add 1 minced garlic cloves along with 1 tablespoon of minced ginger. Stir for about 10 seconds.
Then add 4 tablespoons of brown sugar, 1 cup of low-sodium soy sauce, 1/4 teaspoon of sesame oil, and 1/2 cup water. Bring to a boil then set the sauce aside. 
Then add the sauce and bring the chicken to a simmer. 
Slice two bunches of green onion and stir it into the Mongolian chicken for a few minutes. 
Notes
Time-saving tips
Make the Mongolian sauce ahead of time- You can prepare the sauce in advance and keep it in a container with a lid until you're ready to warm it up and make the rest of the dish.
Cut up the meat and veggies in advance- You can save time by prepping the vegetables and chicken, then putting everything together before dinner.
Cook the chicken in batches- Chicken cooks fastest when it's not touching other things, so separate the chicken into batches so each piece cooks quickly and crisply.