Preheat the oven to 200°C (410°F). Line rectangular baking pan with parchment paper and set aside.
Place the cauliflower rice into a microwave bowl and cook for 3 minutes.
Transfer the cauliflower into a strainer and allow to drain the excess cauliflower liquid. You can also pat the cauliflower down using a paper towel or cloth.
Beat the egg in a medium-size bowl, then add the cauliflower rice and mozzarella cheese and mix together to combine.
Using a 1/4 cup measuring cup, fill the measuring cup with the cauliflower mixture, and using the back of a spoon, compact it down.
Transfer it by flipping over the measuring cup onto the baking sheet separating each hash brown about 2-3 inches apart.
Using your hands, gently flatten each to about 1/2 inch in thickness.
Place into the oven and bake for 25-30 minutes or until lightly golden brown.
Serve with some full-fat sour cream and a sprinkle of parsley or cilantro.