Preheat oven to 200C/390F.
If you have time, soak cashews in water overnight. For the quick version, boil cashews for 15 mins, then rinse under cold water and drain. *Note - if you do not have a high powered blender, I'd recommend soaking the cashews overnight or boiling them for 25 minutes to make them extra soft and to get the sauce as silky smooth as possible.
Prepare vegetables: cut cauliflower into florets, peel pumpkin and cube into medium size chunks. Dice onion and mince garlic.
Combine all spice mix ingredients. Spread cauliflower and pumpkin onto two large roasting trays. Drizzle with olive oil, then coat with spice mix, using your hands to ensure even coverage. Roast for 25-35 minutes, until cooked through and golden on the outside. The cauliflower should be very soft and be easily pierced by a fork.
Combine topping ingredients in a medium mixing bowl and mix well. Spread into a thin layer on a baking tray and bake in the oven for 10-15 minutes until golden and crispy.
Melt margarine in a mediuim saucepan over medium heat. Add diced onion and stir for 2 minutes until fragrant, then add garlic and stir for a 1 more minute. Add cashews, flour and nutritional yeast and stir until well coated.
Muddle miso paste and vegetable stock together.
Gradually add vegetable stock/miso muddle, apple cider vinegar and soy milk, stirring constantly. Simmer for 5-10 minutes until mixture has thickened. Turn off heat.
Add the sauce plus the roasted pumpkin and cauliflower to a high speed blender. Blitz until smooth, adding an extra splash of soy milk if the sauce is too thick.
Combine sauce with cooked pasta of choice, serve and top with the crispy panko crumbs.