Peel and dice the potatoes. Cook in salted water for 5 minutes. Divide the cauliflower into florets and cook for 5 minutes. Put the potatoes first, then the cauliflower in a baking dish.
Chop the smoked tofu in a blender or crumble it with a fork. Fry in sufficient oil until crispy. Add the onions and sauté. Mix the remaining ingredients in a bowl and pour over the mince. Continue frying the meat until the liquid has boiled off and then pour over the cauliflower.
Melt the margarine in a small saucepan and stir in the flour with a whisk. Gradually add the soy milk and the stock until the sauce has the desired consistency. Finally stir in the mustard and yeast flakes. Season the melted cheese with salt and pepper and pour over the casserole.
Bake in the oven at 180 degrees for 30 minutes until the cheese melts brown.