Preheat oven to 425 degrees Fahrenheit. Line a baking sheet with foil and set aside. Add cauliflower, sweet potato, rosemary, garlic, salt, and black pepper to a large bowl and stir. Add enough oil and stir to make sure all pieces are coated with a little oil. Place on baking sheet and cook for 25 minutes, or until sweet potato is softened. Enjoy :)