Prepare your ingredients for easy assembly. Wash, dry, shave and chop the vegetables and parsley (if you are using it) and grate the parmesan.
Combine the dressing ingredients in a jar and shake thoroughly to emulsify. Taste and adjust according to your preferences. It is a very punchy and bright dressing but it mellows on the sturdy vegetables.
To make the maple chilli walnuts, combine the oil, maple syrup, chilli flakes and some seasoning in a medium pan. Place it over a medium heat and allow it to emulsify a little, then stir in the walnuts to thoroughly coat them in the mixture. Once the liquid has all but evaporated from the pan, transfer the walnuts into a bowl.
To assemble, combine the Brussels sprouts, rocket/arugula, apple, ¾ of the grated parmesan and the parsley (if you are using it). Pour over the dressing (reserving a little to taste if you made the higher volume of dressing). Add ½ the walnuts and stir to thoroughly combine and coat all the ingredients in the dressing. Add the remaining dressing if you made extra and feel the salad needs it.
Decant the salad onto your serving platter, then top it with the remaining parmesan and walnuts. Add a bit of extra seasoning and serve.
Leftovers keep really well in the fridge and this salad can be made ahead. I recommend slicing and adding the apple at the last minute so it doesn’t go brown.