Combine prawns, thousand island dressing and lemon zest in a bowl and refrigerate.
Make a quick pickling liquid by combining the vinegar, orange juice and sugar in a small bowl. Add the shaved fennel and toss. Marinate in fridge for 30 minutes.
To serve, put a pinch of rocket leaves in the base of a glass tumbler. Add the marinated fennel, sliced spring onion and diced avocado. Top with the prawn mixture, 3-4 prawns per glass and a pinch of sumac.