Preheat oven to 425°F.
Chop the cauliflower into bite-size florets.
On a baking sheet, toss the cauliflower florets with olive oil. Then add cumin, dried cilantro, salt, and pepper.
Slice the onion in half and leave the outer skin. Rub a little olive oil on the onions before placing them on the baking sheet as well.
Cut one end off the unpeeled garlic cloves. Wrap the garlic cloves along with a drizzle of olive oil in aluminum foil and place it on the baking sheet with the vegetables.
Place the baking sheet in the oven for 30 minutes.
Reserve a few florets for garnish before dumping the remaining cauliflower into the Vitamix. Remove the outer skin of the onion and the garlic cloves and add to the blender. Pour the vegetable broth into the blender. Blend on the programmed setting for hot soup.
Serve the roasted cauliflower soup in a bowl and top with reserved roasted cauliflower florets and parsley (optional).