Step 1

Place stock in a medium saucepan. Bring to a simmer over medium-high heat. Add chicken (see note). Cook, uncovered, for 10 minutes. Turn off heat. Stand, uncovered, for 5 minutes. Remove chicken from poaching liquid and place on a plate. Discard poaching liquid. Rest chicken, covered, for 5 minutes. Shred chicken.

Step 2

Meanwhile, brush corn with oil. Heat a large frying pan over medium-high heat. Cook corn for 6 to 8 minutes, turning, until charred. Transfer to a large plate. Cut kernels from corn.

Step 3

Dressing: Combine mayonnaise, tarragon, vinegar, mustard and 2 tablespoons water in a large bowl. Season with salt and pepper. Reserve 1/3 of the dressing.

Step 4

Add cabbages, corn, carrot, spring onion and chicken to the dressing. Toss to combine. Transfer to a large serving platter. Top with avocado. Drizzle with reserved dressing. Serve sprinkled with extra spring onion.