Thaw or cook the frozen cauliflower rice according to package directions, about 4-5 minutes in the microwave, then drain any excess moisture using a fine-mesh strainer or clean kitchen towel.
In a large skillet over medium heat, melt the butter until foaming, about 2 minutes.
Add the minced garlic to the melted butter and stir constantly for 1-2 minutes until fragrant and softened.
Add the thawed cauliflower rice to the skillet and stir to coat evenly in butter and garlic, cooking for 3-4 minutes over medium heat.
Remove from heat and immediately stir in the grated parmesan until melted and evenly distributed.
Taste and season with salt and black pepper as needed, then sprinkle red pepper flakes over the top if desired before serving.