Orange zest is the coloured, outside portion of the orange peel. It brings a nice citrusy flavour to the halwa here. All you need to do is grate the colourful part of the peel, only twice using a handheld grater and not the white part. The white part has a bitter flavour and hence should be avoided.
Heat some ghee (2-3 tbsp) in a pan. Then add 4-5 almonds, 4-5 pistachios and 4-5 cashews in it. Roast on low flame until the nuts are lightly golden. Then use them to garnish the prepared Halwa.