Start by cutting your boneless chicken breasts into bite-sized pieces. In a large bowl, whisk together the egg, sunflower oil, salt, and pepper. Add in the chicken pieces and stir until well coated.

In another bowl, combine the cornstarch and flour. Dredge each piece of marinated chicken in the cornstarch-flour mix until fully coated. Set aside.

In a medium saucepan over medium heat, combine white distilled vinegar, cane sugar, water, soy sauce, crushed red pepper flakes, garlic, ginger zest, orange juice concentrate, sesame oil, and rice apple vinegar. Bring to a gentle simmer until the sugar dissolves.

Mix one tablespoon of cornstarch with two tablespoons of water until smooth. Slowly pour this into your simmering sauce while whisking continuously. Simmer for another minute until thickened.

In a deep skillet or pot over medium-high heat, add enough oil for frying. Once hot, carefully place several pieces of coated chicken into the oil. Fry until golden brown and crispy on all sides, about four to five minutes per batch.

Once all chicken is fried, return them to the pan with the prepared sauce over low heat. Gently toss to coat every piece thoroughly.