Prepare the dressing 30 minutes ahead of time by combining the brown sugar, soy sauce, sesame oil, vegetable oil and rice vinegar in a small jar with a tight fitting lid. Shake well.
Heat a frying pan over medium high heat with a few tablespoons of oil and break off bits of the noodles and fry them. They will puff up in the pan, so only add a few at a time. As they begin to puff up, remove and drain them on kitchen roll.
In a large bowl, combine the lettuce, chicken, spring onions and sesame seeds. Leave in the fridge to chill about 10 minutes. Just before serving add the cooked rice noodles and toss with desired amount of dressing. Serve immediately in large bowls.