In a medium size mixing bowl, whisk together the hoisin sauce, rice vinegar, soy sauce, brown sugar, minced garlic, ground ginger, red pepper flakes, and 2 tsp. cornstarch. Set this sauce aside.

In a large ziplock bag, combine the flour, 3/4 cup cornstarch, salt, and pepper. Shake the bag well to mix the ingredients.

In a medium size mixing bowl, add the cubed chicken and beaten egg whites. Toss the chicken to coat it evenly in the egg whites.

Heat a large skillet over medium-high heat and add 1/2 cup of vegetable oil.

Using a large slotted spoon, scoop up some chicken pieces, allowing any excess egg whites to drip off, and drop them into the ziplock bag. Shake the bag until the chicken is evenly coated.

Once the oil is hot, fry the chicken in batches. Avoid overcrowding the skillet. Cook until the chicken is golden brown and fully cooked through. Remove the fried chicken and place it on a sheet pan lined with paper towels.

After all the chicken is fried, wipe the skillet with a paper towel to remove any excess oil.

Pour the sauce into the skillet and let it simmer until it starts to thicken.

Add the fried chicken to the skillet and toss to coat all the chicken evenly in the sauce.

Serve immediately with white or brown rice and garnish with chopped green onions.