Preheat the oven to 220°C/fan 200°C/gas mark 6. Place the cauliflower florets on 2 large baking trays, drizzle with 2 tbsp oil and season well with salt and pepper. Roast for 20 minutes, remove from the oven and leave to cool for 20 minutes.
Bring a large pan of salted water to boil. Reduce the heat to a very light simmer.
Heat the remaining oil in a large frying pan and add the mushrooms, thyme and seasoning. Fry for 5 minutes until browned, then transfer to a plate and cover with foil. Add the spinach to the pan and leave to wilt for 2 minutes, stirring occasionally. Transfer to the same plate and recover.
Blitz the cooled, roasted cauliflower in a food processor until it resembles rice. Transfer to the frying pan along with the stock. Bring to the boil and simmer for 10 minutes, then add the lemon juice and season well to taste.
Meanwhile, add the white wine vinegar to the simmering water. Crack an egg into a ramekin and drop the egg swiftly into the water. Repeat with the remaining eggs and poach for 3-4 minutes. Remove the eggs on to some kitchen paper with a slotted spoon. Serve the porridge topped with wilted spinach, mushrooms, a poached egg and a sprinkling of parsley and parmesan.