Preheat the oven to gas 6, 200ºC, fan 180ºC.
Unroll the pastry sheet on a floured surface and trim the edges to neaten. Cut the sheet into 6 squares. Take a square and, ½cm in from the edge, cut a border (cutting right through the pastry), starting from a corner point and stopping 1cm short of the adjacent corner (as indicated by the dotted line in the diagram, below right). Repeat with the opposite side. This gives a ‘frame' that's still attached by opposite corners to the inner pastry square.
Now pull the opposite, cut corners of the pastry frame towards each other, passing one under the other, then stick them down at opposite corners with a little water. Press the borders down on the square, then prick the centre of the square with a fork. Repeat with the other squares. Bake all the pastry cases for 15-20 minutes or until puffed and golden (the doubled borders will rise to make a compartment for the filling).
Meanwhile, whisk the lime juice, olive oil, paprika, sugar and Tabasco and add the prawns and spring onions. Stir and leave to marinate while the pastry cooks.
4 Put a cooked pastry case on each plate, add the avocado and coriander to the prawn mixture and divide the mixture between the cases. Keep a bit of dressing back to spoon over at the end. Serve immediately to ensure the pastry remains crisp, along with some wild rocket and cherry tomatoes.