French open grilled prawn mornay sandwiches

INGREDIENTS
16 cooked Australian prawns, peeled
1 sourdough loaf, cut into thick slices
Béchamel sauce
50 g butter
¼ cup flour
1 ½ cup milk
1 tablespoon dijon
1 cup gruyere cheese
Quick cucumber pickle
1 Lebanese cucumber, cut into ribbons
½ cup white vinegar
¼ cup sugar
1 teaspoon salt
1 tablespoon dill frond
For quick cucumber pickle: place vinegar, sugar and salt in a bowl and stir until sugar dissolves, pour over cucumber ribbons and stir through dill.
To make béchamel: melt butter in a saucepan over medium heat, add flour and stir for 1min. Slowly add milk, whisking until smooth. Cook, stirring until thickened. Add dijon and gruyere and stir until melted. Season to taste.
Heat oven grill to high. Spread each slice of sourdough with béchamel and place under grill until golden and bubbly. Top with prawns, pickled cucumber and dill and serve.
Makes 4 Sandwiches