In a large bowl, combine flour, cornstarch, salt, and pepper. Whisk in the egg, sparkling water, and sesame oil until smooth. Add the chicken pieces and toss to coat evenly. Cover the bowl and refrigerate for at least 30 minutes to marinate.
Heat oil about 1/2 to 1 inch deep in a large wok or Dutch oven to 350°F. Working in batches, add a few pieces of the battered chicken to the preheated oil. Cook, turning occasionally, until the chicken is golden brown and cooked through, about 5-6 minutes. Transfer the fried chicken pieces to a paper towel-lined sheet pan to drain. Repeat with the remaining chicken pieces.
In a large skillet, heat canola oil over medium-high heat. Add the red pepper flakes, garlic, and ginger, and cook for 30-60 seconds or until fragrant. Stir in the sugar, brown sugar, rice vinegar, orange juice, soy sauce, and orange zest. Stir until the sugars dissolve and the mixture begins to bubble.
In a small bowl, whisk together the water and cornstarch until smooth. Add the mixture to the sauce and stir until it thickens, about 1-2 minutes.
Add the fried chicken pieces to the sauce and toss gently to coat. Serve with cooked rice, and top with sliced green onions and toasted sesame seeds.