Preheat oil to 350 degrees in a fry safe skillet. For best results, use a thermometer to maintain accurate oil temperature. Nearby, place a cooling rack atop of baking sheet as a landing space for cooked chicken.
Prepare sauce by combining all sauce ingredients into a saucepan (withholding cornstarch slurry). Bring to a simmering boil until sugar dissolves. Combine the cornstarch+water slurry and add to the sauce, whisk to incorporate and simmer until thickened. Keep warm while preparing the chicken.
Dust Chicken: Place 1/2 cup of cornstarch into a medium bowl and toss chicken chunks in the cornstarch to coat.
Make cold batter by whisking together flour, salt, cornstarch and baking powder in a separate medium bowl. Pour in about ~7 tablespoons of COLD soda water then whisk just a few times until combined, a few lumps are ok - don’t overmix.
1st Fry: dunk a handful of chicken pieces into the batter, turning to coat each piece, place one at a time into the oil. Fry for 3 minutes until light golden brown, remove them and drain on a cooling rack. Repeat with remaining chicken.
2nd Fry: bring oil back to temperature (this takes about 5 minutes or so) and again working in batches, add the chicken back into the oil to fry 90 seconds or until medium-golden brown and return to cooling rack to drain excess oil.
Add handfuls of fully coated chicken into prepared warm sauce, tumbling around quickly to coat, repeating with remaining chicken.
Serve over a bed of warm rice and top with grated orange peel and diced green onions and a few spoonfuls of extra sauce.