Cabbage, prawn and four-bean salad

Place 24 large cooked king prawns (shelled and deveined) in a large bowl. Add 2 cups cabbage (finely shredded), 1 ripe grapefruit (peeled and segmented), 400g can four-bean mix (rinsed and drained) and 1/2 bunch watercress sprigs and toss gently. In a bowl, whisk 1/2 cup extra virgin olive oil, 2 tbsp red wine vinegar, 1 tsp Dijon mustard, 1/2 tsp caster sugar, salt and pepper. Pour dressing over salad and toss gently to combine. Divide salad between four plates and top each with 50g salmon roe.