Heat a medium-sized stockpot over medium-high. When the pot is hot, add the oil and let it heat until shimmering. Add the onion and celery and turn the heat down to medium. Stir and cook until the vegetables are translucent, 3 to 4 minutes. Add the kosher salt and stir well.
Add the cauliflower rice and cook until fully defrosted if using frozen and slightly translu-cent if using fresh. Then add the heavy cream and water. Bring the mixture to a gentle boil.
As soon as it comes to a boil, place the hot mixture into a blender and blend on high until very smooth (you can also use an immersion blender). If your blender has a soup setting, use that to puree. Taste the soup, adding more salt to taste.
Place the pine nuts and sunflower seeds in a dry, small, nonstick sauté pan. Heat over medium heat and toast the nuts until browned, about 1 to 2 minutes. Mix in the chia seeds and parsley.
Divide the soup between four bowls and top with the toasted nut topping.