Mix the marinade ingredients in a small bowl and set aside.
Add the chicken pieces and marinade to a gallon sized storage or freezer bag. Make sure all the chicken is covered with the marinade. Let marinate for 20 minutes.
In another bowl mix together the chicken stock, soy sauce and sugar.
Add the flour to a separate large bowl. Pour the chicken and marinade into the bowl with the flour. Use your hands or a large spoon to mix the chicken and marinade with the flour to form a craggy coating. It’s will get kind of gooey but don’t worry about it, that’s exactly how it should be.
In a separate bowl, add the lemon juice and zest.
Fill a wok or frying pan to about 1/3 full with vegetable oil on high heat. When the oil is hot enough for frying at 325°F, shake excess flour from the chicken pieces and add to the pan. Cook chicken pieces in 2 or 3 batches for about 2-3 minutes on each side or until golden brown on each side. Remove from pan and drain on paper towels.
In another saucepan on medium heat, add 1 tablespoon of oil, garlic and ginger. Cook for about 10 seconds or until fragrant. Then add the chicken stock mixture. Cook for 2-3 minutes until the sugar has dissolved. Then add the lemon juice and zest. Simmer for another minute before adding the cornstarch mixture. Cook for another 4-5 minutes or until sauce has slightly thickened. Add the chicken pieces and toss until evenly coated. Serve over rice or noodles.