In a medium bowl, put all the ingredients for the marinade and stir to combine. Add the duck, cover with plastic wrap and leave to marinate for 30 minutes or as long as overnight.
While the duck marinates, combine the salsa ingredients in a medium bowl. Toss to combine and season to taste with sea salt. Set aside in refrigerator until ready to serve.
Heat a wok or pan over a high heat and add one tablespoon vegetable oil. Place the duck into the wok or pan, skin side down, and fry for 3-4 minutes until the skin is brown and crisp. Turn breasts and reduce heat to medium. Cover and cook for four minutes.
Remove the duck and let rest for five minutes. Chop duck into bite-sized pieces, then dust in the cornstarch and coat well.
Heat a wok or pan over a high heat and fill to a quarter of its depth with peanut oil. Heat the oil to 180°C or until a cube of bread dropped in turns golden brown in 15 seconds. Place the duck pieces in a spider/scoop, lower into the oil and fry until crispy and golden brown. Remove from the pan and drain on paper towels.
To serve, spoon some crispy duck onto a tortilla and top with some salsa. Serve with small bowls of cilantro, flaked sea salt and dried chilli flakes so guests can season their own and help themselves.
Tip: Ensure your wok is stable before deep-frying.