Slice the rolls down the middle, being careful not to cut all the way through, to create space for the filling. Butter the insides, wrap them in aluminum foil, and toast in a toaster oven or oven for a few minutes. Keep warm until ready to serve.
Make diagonal cuts on the surface of the sausages. Heat 1 teaspoon of oil in a frying pan over medium heat and cook the sausages until browned and cooked through.
In a clean pan, heat 1 teaspoon of oil over medium heat. Cook the shredded cabbage until softened. Season with curry powder, rice vinegar, and a pinch of salt.
Fill the roll with the cooked cabbage, top with a sausage, and squeeze on some ketchup.