Zest first: Zest 3 oranges on a fine grater, taking only the orange layer and stopping before the white pith - pith is bitter and cannot be fixed later. Then juice one of them for the 1/4 cup.
Make the batter: Whisk the eggs, coconut flour, salt, pepper and chili flakes until smooth. It thickens as it sits; loosen with a splash of water if it goes past thick pancake batter.
Dry the chicken: Pat the cubes dry with paper towel. Wet chicken sheds its coating in the oil.
Fry in batches: Heat the oil in a deep pan over medium-high to about 350°F. Lift each piece from the batter, let the excess drip off, and fry 3-4 minutes, turning often, until deep golden. Work in batches of 6-8 pieces so the oil temperature holds. Drain on paper towels.
Build the sauce: Combine the orange juice, zest, soy sauce, rice vinegar, sweetener, water, garlic and ginger in a saucepan. Simmer over medium-high for 3 minutes.
Thicken: Sprinkle the xanthan gum across the surface while whisking constantly - never tip it in from a spoon or it clumps into gel beads. Whisk 1-2 minutes until glossy and coating, then pull off the heat. It thickens further as it cools.
Toss and serve: Pour the sauce over the fried chicken and toss to coat. Serve immediately - the crust softens once the sauce is on.