In a large bowl, combine the chicken pieces, salt, black pepper, garlic powder, onion powder, and cayenne pepper (if using). Mix well to coat the chicken evenly. Let marinate for 15-30 minutes for better flavor.

In a separate bowl, mix together the cornstarch and flour. Dredge each piece of marinated chicken in the flour mixture, shaking off any excess.

Heat the vegetable oil in a large skillet over medium-high heat. Once hot, carefully add the chicken pieces in a single layer, ensuring not to overcrowd the pan. Fry for about 4-5 minutes per side, or until golden brown and cooked through. You may need to do this in batches.

Once cooked, remove the chicken from the skillet and place it on a paper towel-lined plate to drain excess oil.

Serve the chicken hot, garnished with sliced green onions and lemon wedges on the side.