Bring a large saucepan of salted water to the boil and cook the pumpkin for 15-20 minutes until tender. Drain and allow to steam for a few minutes before mashing with the Parmesan, seasoning and cornflour until smooth.
Take small tablespoons of the mixture and shape into croquettes. Toss in the flour, then dip in the beaten egg and coat in the dried breadcrumbs. Arrange on a lined baking tray and bake for 15-18 minutes until golden and crispy on the outside.
Meanwhile, heat the olive oil in a large, heavy-based sauce pan and sweat the cabbage for 8-10 minutes, stirring occasionally until soft.
Add the tomato, stir once, then add the olives and add a little water. Cover with a lid and simmer for 4-5 minutes over a low heat. Adjust the seasoning if necessary, then spoon onto serving plates. Spoon the cabbage stew onto serving plates and top with the croquettes when ready to serve.