Slice the potatoes thinly, and place in a pan of hot, salted water and simmer for 5 minutes to parboil. Drain and set aside to cool.
Gently fry the onion, add the mushrooms, then then the passata and simmer for 5 minutes. Mix the cornflour with 1 teaspoon water and stir into the tomato sauce. Add the beans, brown sauce and hot dogs.
Pour the hot dog and bean mix into a ovenproof dish, and top with the sliced potatoes. Brush the top of the potatoes with a little oil, or sprinkle on some cheese.
Bake for 20-25 minutes until potato top is golden brown.