First pat the chicken pieces dry with a paper towel, this helps the seasoning stick.
In a gallon sized freezer bag, place the cornstarch, ¾ tablespoon salt, 1 tablespoon black pepper, and Chinese five-spice powder. Shake to mix. Add the chicken and toss the bag until all of the chicken is coated.
In a large frying pan, wok, or heavy skillet over medium-high heat, add the vegetable oil. Heat until the oil is hot.
Carefully add the chicken one piece at a time allowing space between, and fry chicken for 3 minutes, turn and cook for another 3-4 minutes or chicken turns golden brown and the internal temperature is 165. Place the chicken on paper towels to drain and continue to cook in batches until all of the chicken is done.
In a separate skillet over medium heat, add 1 tablespoon oil. To the oil, add the onion and cook for about 5 minutes or until the onion begins to soften, stirring frequently. Stir in the garlic, chiles, and green onions. Continue cooking for an additional 2-3 minutes.
Place the cooked chicken and veggies in the same skillet and stir to coat the chicken with the veggies.
Serve immediately while still hot.