Cut the sausages in half lengthwise, without cutting all the way through.
Grate the cheese on a fine grater.
Finely chop the parsley.
In a bowl, combine mayonnaise, mustard, breadcrumbs and a third of the grated cheese.
Place the sausages in a baking dish with the cuts facing up. Fill the sausages with the cheese and mayonnaise mixture.
Sprinkle the sausages with the remaining cheese.
Place the sausages in the oven for 10 minutes. The cheese should get a golden crust and the sausages should be ready.
Place the finished sausages on a plate, pour ketchup to taste and sprinkle with chopped herbs. Enjoy!