Preheat waffle iron to medium heat.
In a shallow bowl, whisk together eggs, milk, mustard, salt and pepper.
Brush waffle maker melted butter. Build sandwiches: once slice of bread, some cheese, a slice of ham, a slice of turkey, more cheese and another piece of bread. Turn sandwiches in batter and place in waffle iron. Close waffle iron and cook 5 minutes or until golden brown.
Serve with an arugula salad alongside.