Add the frozen cassava to a pot of water and boil until tender. About 15 - 20 minutes.
Once cassava is cooked, drain and let cool until you can handle easily without buying your hands. Cut into cubes and set aside.
In a large skillet, over medium high heat, heat butter, add garlic, onion and carrots, sauce for a minute or two until fragrant and onions are translucent.
Add the cassava and toss to coat the cassava in the butter and the veggies are evenly combined. Cook for a minute or two until the butter in absorbed, season with salt and pepper to taste, then remove from heat and serve.