Prepare the rub by grinding the whole spices to a fine powder (see Note 1).
Prepare the marinade by whisking all marinade ingredients together.
Make a few cuts on the skin side of the duck breasts - try not to cut the meat. Rub them with the five spice blend, place into a zip lock, pour in the marinade and shake to coat. Leave in the fridge for at least half an hour.
Heat a frying pan to medium-high. Add one tbsp olive oil and fry the whole spices (star anise, cardamoms and allspice berries, if using) for 20-40 seconds until fragrant.
Shake the marinade off the duck breasts and briefly pat them dry (see Notes).
Add the duck breasts to the pan skin side down and fry for 1-2 minutes, then flip and fry for another couple of minutes.
Transfer to a roasting dish and roast in a preheated oven skin side up at 190C for 12 minutes for medium.
For the sauce, heat orange and mango juices in a pan. Add 1/2 tbsp balsamic vinegar and 1/2 tsp red chili flakes and reduce over high heat to 1/3.