Mix all the sauce ingredients in a small bowl and set aside.

Combine chicken pieces, vegetable oil, and salt in a big bowl. Mix well and let marinate for 10 to 20 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 heavy duty skillet until hot, until it just starts to smoke. Add chicken all at once and spread out into a single layer in th

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 to a big plate and remove the pan from the stove. Let cool for 2 to 3 minutes.

Place the pan back onto the stove and turn to medium heat. You should still have 1 to 2 tablespoons oil in the pan. Add garlic and ginger. Cook and stir a few times until it releases it's fragrance. Add mushrooms and let them sweat it out for a minute.

Stir the sauce again to dissolve the cornstarch completely. Pour into the pan. Stir and cook until it thickens, when you can draw a line on the bottom with a spatula without the sauce running back immediately.

Add back the chicken pieces, onion, and bell peppers. Stir to coat chicken with sauce, 30 seconds. Transfer everything to a plate immediately.

Serve hot as main over steamed rice.