Measure soy sauce, mustard, honey and the juice of one orange in a zip lock bag big enough to easily accommodate the chicken breast fillets. Mix well with a spoon.
Add the chicken fillets into the bag and close well.
Turn the bag in your hands for a couple of times to get the marinade all over the fillets.
Place the bag in the fridge at least for 8 hours. If possible, flip the bag once during the marinading.
When it's time to prepare dinner, preheat the oven to 200 C.
Move the chicken fillets from the marinade and put them in an oven pan. There is no need to tap them dry or drain.
Spread the rosemary leaves on the fillets and place one orange slice on each fillet.
Roast in the oven for app. 30 minutes or until the chicken is cooked through.
Tips
Serve with quinoa, rice, potatoes, salad.The chicken fillets should be taken to room temperature half an hour before putting them in the oven, but if you don't have the time, just skip that.