In a mixing bowl, combine cornstarch, flour, baking powder, garlic powder, salt and white pepper. Whisk to combine.
Add cold water and egg. Whisk until smooth. Set aside to rest for 5 minutes.
Pour oil into a deep skillet or wok. Place over medium heat.
When oil is heated to 350°F and shimmering, dip chicken pieces into batter.
Allowing excess to drip off, carefully add to hot oil and fry in batches until golden brown and crispy, about 4 - 5 minutes.
Remove to a paper towel-covered plate to drain.
Continue until all chicken is cooked. Set aside and keep warm.
Place a saucepan over medium heat. Add lemon juice, honey, soy sauce, chicken broth, sugar, rice vinegar, ginger and garlic.
Bring to a simmer, stirring occasionally.
Add cornstarch slurry and whisk until sauce thickens.
Stir in sesame oil and red pepper flakes.
Add crispy chicken to lemon sauce, tossing gently to coat.
Transfer to a serving plate and garnish with lemon zest, green onions and sesame seeds.
Serve immediately over steamed rice or alongside stir-fried vegetables for a restaurant-quality meal at home.