In a large bowl, whisk together soy sauce, sugar, crushed garlic, chopped green onion, sesame oil, red chili flakes, white pepper, and cornstarch until well combined. The mixture should be smooth and slightly thickened.

Add cubed chicken breast or thighs to the marinade, ensuring each piece is thoroughly coated. Cover the bowl and let it marinate in the refrigerator for at least 30 minutes, or up to 2 hours.

In a shallow dish, mix together flour, cornstarch, and a pinch of salt. Once the chicken has finished marinating, remove it and let any excess marinade drip off. Dredge each piece in the flour mixture.

In a large skillet, heat about an inch of vegetable oil over medium heat until it reaches around 350°F (175°C).

Carefully add the coated chicken pieces to the hot oil in batches and fry each for about 5-7 minutes, turning occasionally, until golden brown and crispy.

Once cooked, use a slotted spoon to remove the fried chicken and place it on a paper towel-lined plate. Allow to rest to drain excess oil.

If desired, toss the freshly fried chicken in any reserved marinade or simple garlic sauce immediately after frying.

Serve the chicken warm, plated alongside fluffy white rice or fried rice, and garnish with chopped green onions.