Preheat the oven to 180C/350F/Gas 4.
Lightly toast the bread on a baking sheet in the oven. Remove and spread the mustard on one side of the toast.
In a bowl, mix together the grated cheese, Worcestershire sauce and basil leaves, then pile onto the toast, followed by the chopped tomatoes. Return to the oven to cook for 2-3 minutes, or until the cheese is melted and bubbling.
Cut each piece in half and serve immediately.
