Prep the chicken: Cut 2 lbs boneless, skinless chicken thighs (or breasts) into bite-sized pieces. Pat them dry.
Make the batter: In a bowl, whisk together 3 cups flour, 1 cup cornstarch, 1 teaspoon salt, and ½ teaspoon black pepper. In a separate bowl, beat 2 eggs with 2½ cups water and 2 tablespoons vegetable (or avocado) oil, then slowly stir the wet mixture into the dry until smooth. Cover and chill for 30 minutes in the fridge.
Heat the oil: Pour about 2 inches of vegetable oil into a heavy skillet or pot and heat it to 320°F (use a thermometer).
First fry: Dip the chicken pieces into the batter, letting excess drip off, and carefully add them to the hot oil in batches. Fry until just cooked and light golden, about 3–4 minutes. Remove and let drain on a rack or paper towel.
Second fry (for extra crispiness): Increase oil temperature slightly if needed, then return the partially fried chicken to the oil and fry again until deeply golden and very crispy, about 2–3 more minutes. Drain well.
Make the orange sauce: In a saucepan over medium heat, combine juice of 2 oranges, zest from those oranges, 4 tablespoons soy sauce, ½ cup rice vinegar, 2/5 cup packed brown sugar, and 4 minced garlic cloves. Bring to a simmer.
Thicken the sauce: Mix 2 teaspoons cornstarch with 1 tablespoon water to make a slurry, then whisk it into the simmering sauce. Cook until it thickens and becomes glossy.
Toss chicken in sauce: Add the double-fried chicken to the sauce and toss until every piece is well coated.
Garnish & serve: Sprinkle with sesame seeds, chopped green onions, and red pepper flakes if you want that spicy Panda Express-style kick. Serve immediately over rice or noodles.