In a food processor blend the pine nuts, parmesan, basil and salt. Pour in the lemon juice and oil and continue blending to a rough paste.
Mix the pesto into the shredded chicken and set aside.
Brush each slice of bread with garlic butter and place 6 slices brushed side down in a large baking tray. Sprinkle each piece with the cheese mix and then a large spoonful of the pesto chicken, then top with more cheese and the final 6 pieces of bread, butter side up. Cover with another baking tray and press down to squash.
Bake for 20 minutes until the bread has browned and the cheese is molten and delicious.