Combine the cubed chicken thighs with the beaten egg, cornstarch, flour, salt, and black pepper. Cover and marinate for 15 to 30 minutes.

Pour vegetable oil into a deep skillet and heat over medium-high to 350°F (175°C).

Fry marinated chicken in batches for 5 to 7 minutes until golden brown and crispy. Remove and drain on paper towels.

In a bowl, whisk together soy sauce, rice vinegar, granulated sugar, hoisin sauce, chicken broth or water, and cornstarch until smooth.

In the skillet, heat sesame oil and vegetable oil over medium heat. Add minced ginger and garlic; sauté until fragrant.

Pour the sauce mixture into the skillet, stirring to incorporate the ginger and garlic. Simmer for 2 to 3 minutes until thickened.

Stir in red pepper flakes and adjust heat level as desired.

Add the fried chicken back to the skillet, tossing to coat with the sauce.

Simmer the chicken and sauce together for 1 to 2 minutes to meld flavors.

Transfer to a serving platter and garnish with sesame seeds and green onions. Serve over rice.