Add the cornstarch and salt and mix, ensuring every piece of chicken is coated.
Heat enough oil to deep fry the chicken over medium-high heat. The oil is ready when a wooden skewer or chopstick pressed to the bottom of the pan sizzles and forms bubbles.
Fry the chicken, in batches, until golden brown and cooked through (approximately 5-7 minutes). Remove with a slotted spoon and allow to drain on a wire rack set over a sheet pan.
Fry the garlic in a splash of oil until fragrant then add the soy, hoisin, stock, brown sugar and vinegar. Bring to a simmer and cook for 5-7 minutes until thick and glossy.
Add the chicken and cashews to the sauce and toss to coat.
Scatter the spring onion and sesame seeds over the chicken then serve with noodles.