Heat the beans gently in a small saucepan over low heat.
Butter one side of each slice of bread. Place two slices butter-side down in a sandwich toaster or frying pan.
Spoon the hot beans onto the bread, leaving a small gap around the edges. Add a few drops of Worcestershire sauce if using.
Scatter the grated cheese over the beans on each slice.
Top with the remaining bread, butter-side up. Cook for 3-4 minutes on each side until golden and the cheese is melted through.
Cut in half and serve immediately while hot.