Meanwhile, heat the vegetable oil in a large saucepan and gently fry the onion, garlic and carrots for 2-3 minutes, until softened. Add the vegetarian mince, tomatoes and stock. Stir in the curry powder, then add the mushrooms and courgette. Bring to the boil, then reduce the heat and cook, stirring occasionally, for 15-20 minutes. Season with black pepper.
Preheat the grill, warming a large baking dish underneath for a few moments. Meanwhile, drain and mash the potatoes and butternut squash, seasoning with black pepper.
Blend the cornflour with 1 tbsp cold water and add it to the mince mixture, stirring until thickened. Transfer it to the warm baking dish and spoon the vegetable mash on top. Grill for about 8-10 minutes, until browned. Serve.