Preheat the oven to 420F and set a baking sheet aside.
Add the diced tofu to a medium bowl, pour the oil over it, and toss gently with a spatula. Add the cornstarch, nutritional yeast, rosemary, garlic powder, black pepper, and salt to the bowl and toss again until the tofu is evenly coated
Transfer the tofu to the baking sheet and spread it out evenly so it does not touch. Bake on the top rack of the oven for 15 minutes, then remove and flip the tofu. Return the tofu to the oven and bake for an additional 12 to 15 minutes, until golden and crispy
Serve warm. Leftovers can be stored in the refrigerator, in a sealed container, for up to 5 days.