Cut the sirloin slices into bite-sized pieces.
Thinly slice the kabocha squash with the skin on.
Heat oil in a pan and separately sauté the sirloin and kabocha until cooked.
Slice the bread in half and hollow out the inside a bit.
Layer the kabocha and then the sirloin slices on the bread.
Season with salt and pepper and add your preferred sauce.
Top with the other half of the bread to finish the sandwich.