Preheat oven 425 degrees F. Spray casserole dish and set aside
Meanwhile, prepare the Vegan Gravy and set it aside
Trim and discard tough stems and cauliflower leaves, In a medium bowl, mix vegan mayonnaise and dry seasonings to form a paste.
Place cauliflower in a bowl, and smother mayonnaise paste all over the cauliflower head, base, and in between the florets as much as possible..Transfer cauliflower to the casserole dish.
Add potato and carrot chunks to the bowl and toss with the remaining mayo mixture in the base of the bowl. Add seasoned potato, carrots, and half of the vegan gravy to the casserole dish and place them around the cauliflower.
Cover the casserole dish with parchment paper and foil and bake for 1 hour. Meanwhile, prepare the Vegan Gravy and set aside. After 1 hour, remove the cover and reduce oven temperature to 400 degrees and bake for about 20 minutes or until vegetables are tender and golden Brown.
Before serving, smother cauliflower and vegetables with the gravy, garnish with fresh rosemary sprigs and serve.