In a large bowl, combine boneless chicken breasts or thighs with soy sauce, sake, mirin, sesame oil, minced garlic, grated ginger, white pepper, and a pinch of salt. Add an egg white to help the coating adhere. Mix thoroughly until the chicken is evenly coated, then cover and refrigerate for at least 1 hour or overnight.

In a mixing bowl, combine mayonnaise, Thai sweet chili sauce, sriracha, and fresh lemon juice. Whisk until smooth and creamy.

After marinating, remove the chicken from the fridge. Dredge each piece in cornstarch or panko bread crumbs, ensuring it's fully coated on all sides.

In a deep skillet, heat neutral oil to 350°F. Carefully add the coated chicken pieces in batches, cooking for about 5-6 minutes until golden brown. Use a slotted spoon to transfer the cooked chicken to a paper towel-lined plate.

Toss the fried chicken pieces gently in the prepared spicy peanut sauce until evenly coated. Serve immediately.