1.Peel and devein prawns, leaving tails intact. Combine prawns, garlic, juice, cumin, sugar and oil in a large bowl. Cover, refrigerate 10 minutes.
2.Meanwhile, make dressing. Place ingredients in a screw-top jar, shake well. Season to taste.
3.Brush corn with butter, season. Cook corn on a heated oiled char-grill pan (or barbecue), turning, 10 minutes or until browned lightly and just tender. Using a sharp knife, cut corn kernels from cobs. Transfer to a small bowl, cover to keep warm.
4.Meanwhile, heat extra oil in a medium frying pan over medium heat, fry tortilla strips, in two batches, stirring, 2 minutes or until golden. Remove with a slotted spoon, drain on paper towel. Season with salt to taste.
5.Season prawn mixture, cook on heated char-grill pan for 3 minutes, turning halfway, or until just cooked through.
6.Halve avocado, scoop flesh into a large bowl. Add lettuce, radish and three-quarters of the coriander, toss gently to combine. Arrange lettuce mixture on a platter, layer with prawns and corn, then drizzle with dressing.
7.Serve salad topped with tortilla strips and remaining coriander.
The tortilla strips can be prepared a day ahead; cool and store in an airtight container.Note