Heat the oil in a medium saucepan set over medium-high heat. Add the celery and onion and cook 5-7 minutes, or until soft.
Add the cauliflower and stock. Bring to a boil, then reduce heat and simmer 10 minutes, or until the cauliflower is soft. Transfer to a blender; blend on high until smooth.
Return the soup to the pot. Slowly stir in the mozzarella until melted. Add salt to taste.
Serve the soup topped with croutons, smoked paprika, and additional mozzarella shreds.