Preheat the oven to 200C/180C Fan/Gas 6.
Fry the bacon in a hot frying pan until crisp. Set aside.
Keeping the tails on, remove and discard the black digestive tract from the prawns. Butterfly them by making an incision down the back of the prawns without cutting through to enable you to open them out.
Combine the butter, garlic, chilli, a tablespoon of chopped parsley, lemon juice and Tabasco sauce. Season with salt.
Divide the spinach among four individual gratin dishes and spoon over the cooked bacon.
Divide the prawns among the gratin dishes and spread the flavoured butter over them.
Mix the breadcrumbs, lemon zest, remaining parsley and Parmesan together in a bowl and sprinkle the mixture over the prawns.
Bake for 6–8 minutes, or until the prawns turn pink and the breadcrumbs are golden-brown. Serve with lemon slices.