Pour the olive oil into a large non stick frying pan and heat it over a medium flame. When the oil is hot, fry the slices of ciabatta on both sides until lightly coloured but still soft inside. Drain on kitchen paper, keep warm and reserve the pan.
You need 3-4 tbsps oil in the pan so add or discard as necessary. Return the pan to a medium heat and tip in the chopped celery and garlic. Fry for 2-3 minutes until the garlic is a light nutty brown, stirring often. Be careful not to let the garlic burn.
Add the mushrooms and some salt, and stir until all the chunks are coated in oil. Fry for about 3 minutes, stirring frequently, until the mushrooms have started to wilt. Now stir in the prawns and chopped parsley, grind on some black pepper and tosx the prawns for no more than a minute to heat through.
Put the slices of ciabatta on warmed plates and pile the prawn mixture and juices on top. Serve immediately.