Melt butter and brush inside a 9x13 inch baking dish with some of it.
Assemble 8 "sandwiches" in this order, bread, slice of meat, slice of cheese, slice of meat, slice of cheese, then bread and fit them into the baking dish in one layer. Brush the top layer with some of the melted butter.
In a medium bowl, whisk the eggs with the Worcestershire sauce, salt, mustard, hot sauce, and black pepper. Whisk in the milk and pour over the bread layers in the casserole. Sprinkle the top with red and green bell pepper, and the spring onion.
Wrap with plastic wrap and refrigerate at least 1 hour or overnight to absorb the custard mixture.
When ready to bake, preheat your oven to 180 C. Melt the remaining butter and mix with the crushed cereal. Sprinkle evenly over the top of the casserole and bake for 1 hour until the center is set. Let stand for at least 10 minutes before cutting into squares to serve.