Place the flour in a large bowl and add the yeast to one side and the salt and sugar to the other. Mix in the olive oil, pumpkin puree and water, it should form a slightly sticky dough. Turn out onto an un-floured work surface and knead for about 10 minutes until smooth, elastic and no longer sticky; if the dough seems too wet you can add a little bit more flour. Place the dough in a lightly oiled bowl, cover and set aside to rise until doubled in size, 1-2 hours. You can also place the dough in the fridge to rise overnight if you prefer.
While the dough is rising prepare the toppings. Preheat the oven to 200C/400F/gas mark 6. Spread the prepared pumpkin out in a roasting tray, scatter over the onion, rosemary and cumin, drizzle with olive oil and salt and pepper, toss everything together to coat then roast for about 20-30 minutes until tender; set aside.
To make the tomato sauce, place the passata, olive oil, garlic and red pepper flakes in a small saucepan. Bring up to the boil then simmer gently for 15-20 minutes until reduced and thickened; season to taste with salt and pepper.
Turn the oven up to max (245C/475F/gas mark 9). Sprinkle a worksurface with a mixture of flour and semolina. divide the risen dough in half and shape each half into a ball. Roll each ball out thinly to about 25cm diameter and place each one on a baking sheet.
Spread a couple of spoonfuls of the tomato sauce over each base, scatter over the pumpkin and onion then top with crumbled goats cheese and mozzarella slices. Sprinkle with oregano, rosemary, red pepper flakes and salt and pepper.
Bake the pizzas for 20-25 minutes, rotating the trays halfway through, until crisp and browned. Scatter with fresh basil leaves to serve.