Preheat oven to 200°C (390°F). To make the lime mayonnaise, place the mayonnaise, lime rind and juice, salt and pepper in a bowl and stir well to combine. Set aside.
Place the prawns, eggwhite, chilli, salt and pepper in a food processor and process until smooth. Brush both sides of the bread with butter. Place one of the slices on a baking tray lined with non-stick baking paper, spread with the prawn mixture, top with coriander and zucchini. Sandwich with the remaining bread and sprinkle with sesame seeds. Use a knife to score the bread into 16 triangles. Bake for 10–15 minutes or until golden and crunchy. Serve with lime mayonnaise. Makes 16.