Preheat the oven to 430°F (220°C).
Add cauliflower florets to a mixing bowl along with olive oil, sea salt and black pepper and toss the cauliflower florets so that they are lightly coated in the oil and spices.
Transfer to a roasting pan or a parchment lined tray and bake in the oven at 430°F for 20 minutes. Remove the cauliflower from the oven and then turn the oven down to 400°F.
While the cauliflower is roasting prepare your cheese sauce. Add vegan butter to a saucepan on medium to high heat and when melted add in all purpose flour. Fry the flour in the vegan butter briefly.
Add the soy milk all at once and whisk it in. Bring to the boil stirring and whisking constantly. When it boils keep stirring for a few minutes until it has thickened noticeably.
Remove from the heat, add nutritional yeast, dijon mustard, onion powder, garlic powder and salt and whisk in.
Place the roasted cauliflower into a mixing bowl, pour over the cheese sauce and toss the cauliflower gently in the sauce.
Prepare your breadcrumbs by adding them to a bowl with melted vegan butter and toss the breadcrumbs with the butter so that they’re lightly coated.
Transfer the roasted cauliflower and sauce to a 9x13 baking dish and smooth down.
Spread the breadcrumbs evenly over the top.
Bake in the oven (uncovered) at 400°F for 25-30 minutes until browned on top.
Serve topped with some fresh chopped parsley and ground black pepper.