Unwrap the pre-cooked polenta and pat it dry. Slice it lengthwise into even fry-shaped pieces.
Put the polenta fries into a bowl. Add olive oil and sprinkle on garlic powder, onion powder, rosemary, salt, and pepper. Toss gently to coat evenly.
Arrange the fries in a single layer on a parchment-lined baking sheet. Bake for 30 to 40 minutes, flipping them halfway through, until they are golden and crispy.