Begin by cutting the chicken breasts into bite-sized pieces.
In a mixing bowl, combine the flour, cornstarch, garlic powder, onion powder, salt, and black pepper.
Coat each piece of chicken in the flour mixture, shaking off any excess.
Heat the vegetable oil in a frying pan over medium-high heat.
Add the coated chicken pieces to the pan in batches, ensuring not to overcrowd. Fry until golden brown and cooked through, about 5-7 minutes per side.
Once cooked, transfer the chicken to a paper towel-lined plate to drain excess oil.
In a saucepan over medium heat, combine soy sauce, brown sugar, rice vinegar, and sesame oil. Whisk until the sugar dissolves.
In a small bowl, mix 1 tablespoon of cornstarch with 2 tablespoons of water to create a slurry. Add this to the saucepan.
Stir continuously until the sauce thickens, about 2-3 minutes. Remove from heat.
Drizzle the teriyaki sauce over the crispy chicken, or toss to coat.
Serve garnished with sliced green onions and sesame seeds.