Preheat oven to 200°C and line an oven tray with baking paper.
Blitz cauliflower in a food processor until it has a fine, crumbly texture, like rice. Alternatively, you can grate the cauliflower.
Place crumbly cauliflower in a large bowl and microwave, uncovered, for about 6 minutes, or place on lined oven tray and bake for about 15 minutes, until just tender. Remove and transfer to a clean tea towel. When cool enough to handle, wring tea towel tightly to squeeze out as much water as you can.
Tip cauliflower into a large bowl, mix in egg, Parmesan, garlic and dried herbs/spices and season well with salt and pepper. Spoon mixture into the centre of the lined tray and spread out and flatten to make a circular or rustic pizza shape approximately 0.5cm thick. Bake for 30-40 minutes or until firm and golden around the edges.
Increase oven temperature to 220°C. Spread pizza sauce over the baked pizza crust and scatter over half of the mozzarella. Top with mushrooms and pumpkin ribbons, drizzle with olive oil, scatter with chilli and rosemary, then sprinkle with remaining mozzarella. Return to the oven to bake for 6-10 minutes or until the pumpkin is coloured and cheese bubbling.
To serve, cut pizza into 6 even slices. Serve with green salad.