Boil the jug with water and preheat the oven on fan bake at 200°C (390°F), then chop your cauliflower into bite-sized pieces.
Put the pasta in a pot and cover with boiling water, then place the cauli on top in a steamer attachment (if you have one). Cook both for 5-7 minutes. If you don't have a steamer you can cook the cauli in a separate pot with 1/2 cup of extra boiling water.
While these steam, heat the oil in a large flat pan (oven-proof if possible), and saute the onion and garlic for five minutes until light brown and caramelised.
Blend all the topping ingredients in a blender until they form a crumb but still with some texture - set aside.
Drain the pasta and cauliflower reserving 2 cups of cooking water. Pour the pasta into the pan with the onions while still on a low heat.
Meanwhile, put the cauli in your blender with the 2 cups of cooking water and all remaining sauce ingredients (cashews, nutritional yeast, mustard, pepper and salt) except parsley. Blend until super creamy then pour into your pasta pan, adding the parsley, and stir while still on low for 2 minutes until everything heats through and the sauce begins to thicken.
Pour over the sunflower seed topping, then bake in the oven for 10 minutes until golden and crunchy on top.
Serve with a simple garden salad and get in quick if you want any chance of seconds!