Trim the chicken thighs and cut them into 1-inch cubes. Dredge in cornstarch and set aside.

In a medium bowl, combine cold water, soy sauce, rice vinegar, hoisin sauce, and sugar. Whisk in cornstarch until smooth.

Heat olive oil in a large skillet. Fry the coated chicken in batches for 4-5 minutes until golden brown.

In the same skillet, add garlic, ginger, and red pepper flakes. Sauté for 30 seconds until fragrant.

Pour the sauce into the skillet and simmer for 1 minute until thickened.

Return the fried chicken to the skillet and toss it in the sauce until evenly coated.

Transfer to a serving plate, optionally garnish with sesame seeds, and serve hot.