Preheat the oven at 200C/400F/Gas 6. Peel, seed and roughly chop the butternut squash. Put the pieces of squash in a steamer basket and place over boiling water. Steam for 20-30 minutes until fully tender. They must be soft enough to mash.
Peel and roughly chop the onion. Peel and finely slice the garlic. Warm a couple of tablespoons of the olive oil in a large pan, then add the onion and garlic and cook until pale gold. Cut the mushrooms into thick slices or quarters and add to the pan with the leaves from the thyme sprigs. Fry until softened, then transfer to a mixing bowl.
Add a further tablespoon of oil to the pan, then, as soon as it starts to sizzle, add the minced turkey. Season generously with salt and pepper and then stir in a couple of heaped tablespoons of flour. Cook for 2-3 minutes, then pour in the red wine and a few shakes of Worcestershire sauce. Simmer at a low temperature for 5 minutes then add the mushrooms and onions. Continue cooking for 5 minutes then tip into a baking dish.
Mash the cooked squash with a potato masher then stir in a generous knob of butter and the grated orange zest, to taste. Season with salt and pepper.
Pile the mash on top of the turkey, dot with more of the butter, then bake for 35-45 minutes, or until the mash is lightly browned and slightly crisp on top.