Preheat oven to 180°c and line a baking tin with greaseproof paper.
Sieve the flour and cacao powder into a large mixing bowl then stir in the sugar and orange zest and candied orange pieces.
Melt the chocolate either in a microwave or in a heatproof bowl over a pan of boiling water. If you're using a microwave, check it every 15 seconds to make sure it doesn’t burn.
Put the orange juice in a measuring cup then top the cup up with chocolate soy milk until you have one full cup of liquid in total.
Stir in the cup of liquid, sunflower oil, orange oil, and melted chocolate. Mix thoroughly to combine.
Pour the brownie batter into the prepared baking tin and place in the oven for 20-25 minutes. When done they should be cooked on the outside and slightly gooey in the centre.
Leave to cool for 5-10 minutes then place on a wire cooling rack before slicing.