Cut chicken into 1-inch cubes.

In a medium bowl, mix together the flour, cornstarch, salt and pepper. Add the egg, oil and water, whisking until smooth.

Add the chicken cubes to the mixture, making sure the chicken gets thoroughly coated. Cover and chill for 30 minutes in the fridge. (If you're in a hurry, 10 minutes will do.)

In a medium saucepan or deep fryer, add 2 inches of oil and heat to 350˚F (177˚C). Line a plate with paper towels and set aside.

Add the marinated chicken cubes in batches of about 10-15 pieces, shaking off excess batter if needed. Deep fry for 2-3 minutes until golden, turning halfway through with a slotted spoon for even browning.**

Remove to the plate and cover with foil to keep warm while you make the sauce.

To a medium saucepan, add orange juice, orange zest, soy sauce, vinegar, brown sugar, and garlic.

Place the saucepan over medium heat and bring to a low boil. Carefully taste a few drops and adjust sugar, soy sauce and vinegar to suit your preference.

Mix the cornstarch and water in a cup to make a slurry and pour into the sauce. Stir constantly until the sauce coats the back of a spoon. (This can take as little as 30 seconds or as long as several minutes.)

Add the fried chicken and toss until the sauce coats it thoroughly.

Garnish with optional sesame seeds, green onions and red pepper flakes. Serve immediately.