Combine chicken pieces, vegetable oil, and salt in a big bowl. Mix well and let marinate for 10 to 15 minutes.
Add the beaten egg into the bowl with the chicken. Stir to mix well. Add cornstarch. Stir to coat chicken, until it forms an uneven coating with a little dry cornstarch left unattached.
Heat oil in a large nonstick skillet over medium high heat until hot. Add chicken all at once and spread out into a single layer in the skillet. Separate chicken pieces with a pair of tongs or chopsticks.
Cook without touching the chicken for 2 to 3 minutes, or until the bottom turns golden. Flip to brown the other side, 2 to 3 minutes. Transfer chicken into a big plate and remove the pan from the stove. Let cool for 2 to 3 minutes.
Whip the extra oil from the pan by using a few layers of paper towel attached in front a pair of tongs.