Place all ingredients except bread and buttery spread into a medium bowl and mix well.
Divide the filling between 4 bread slices, and top with remaining slices.
Divide the buttery spread between the sandwiches, spreading on the outside of both the top and bottom of each sandwich.
Cook in a pre-heated non-stick pan over medium-low heat until browned, flip and cook other side until browned and filling is warmed through. (Or use a panini press if you have one). Serve immediately.