Combine the cauliflower, 1 1/4 cups of the vegetable broth, 1/2 cup water, the lemon juice and 1/2 teaspoon of the sea salt in a large saucepan. Bring to a boil, lower the heat, cover and simmer until very tender, 15 to 20 minutes.
Meanwhile, heat the coconut oil in a large skillet over medium heat. Add the carrot, celery, onion and the remaining 1/2 teaspoon sea salt and cook until the vegetables are soft, about 15 minutes. Add the garlic and cook until the vegetables are beginning to brown, an additional five minutes. Stir in the herbes de provence, granulated onion and tarragon and cook a few minutes longer. Add the sauteed vegetables to the cauliflower mixture and stir to combine. Remove from the heat.
Combine the sunflower seeds, the remaining 1 1/4 cups vegetable broth and 1/2 cup water in a blender. Puree until very smooth. Working in batches if necessary, add the contents of the saucepan to the blender and puree until smooth and creamy. Pour the finished soup into bowls and garnish with a sprinkling of pepitas and a drizzle of pumpkin seed oil.