Preheat a chargrill on high heat. Lightly brush the corn with a little oil. Cook on the grill, turning, for 8 minutes or until corn is tender. Set aside to cool slightly. Use a sharpe knife to cut the kernels from the cobs.
Meanwhile, combine the prawns with half the taco seasoning and 2 teaspoons of the oil in a large bowl. Cook on the grill for 2 minutes each side or until the prawns curl and change colour. Transfer to a plate.
Whisk the lemon juice, remaining taco seasoning and remaining oil in a jug until well combined.
Combine the prawns, corn, avocado, kidney beans, tomato, onion and lettuce in a large bowl. Drizzle with the dressing and toss to combine. Divide salad among serving plates. Toss with the corn chips and serve.