To Make Batter: In a medium size mixing bowl, whisk together flour, cornstarch, salt and pepper. In a separate small bowl, whisk together seltzer water, egg and 2 Tbsp oil.
Add wet ingredients to the dry ingredients mixing until fully combined. Add chicken pieces, stirring to coat. Cover and chill for 30-60 minutes.
To Fry Chicken: In a deep heavy bottomed pot or Dutch oven heat oil to 350-360°F. Remove chicken from batter allowing excess to drip off. Carefully lower into the hot oil. Cook in batches for 4-6 minutes total turning as needed. Fry until golden brown and cooked through. Remove using a slotted spoon to a paper towel lined sheet pan or platter.
To Make Orange Sauce: Meanwhile, heat 2 Tbsp oil in a deep skillet or heavy bottomed saucepan over medium high heat. Add garlic and red pepper flakes. Cook for 1 minute or just until fragrant.
To the skillet add orange juice, soy sauce, vinegar, 1 tsp sesame oil, granulated sugar, brown sugar and ground ginger. Cook stirring until sugar has completely dissolved.
Dissolve 1/4 cup cornstarch in 1/4 cup cold water in a small bowl. Whisk into the pan. Simmer sauce until thickened over medium heat to a syrup consistency.
Toss chicken pieces in sauce. Serve immediately over rice, garnished with chives.