Bring a large pot of salted water to a boil. Add the cassava and cook until fork-tender, about 15–20 minutes. Frozen cassava can go straight into the boiling water without thawing.
Drain the cassava and let it cool until comfortable to handle. Remove the tough fibrous core from the center, then cut the cassava into bite-sized pieces.
Melt the butter in a large skillet over medium heat. Add the onion and cook until it begins to soften and turn translucent.
Add the grated carrots and cook for another 2–3 minutes, just until they begin to soften.
Add the cassava, garlic powder, onion powder, black pepper, and 1 teaspoon salt. Gently toss until everything is well coated.
Cook for another 3–5 minutes, gently tossing occasionally, until the cassava is heated through and picks up a little color.
Taste and adjust the salt as needed. Serve warm.