Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Drain the firm tofu and press it between heavy plates and paper towels for 10 minutes to extract moisture, then cut into 1-inch cubes.
Wash and peel the potato and carrots, dicing the potato into 1/2-inch cubes and slicing the carrots into 1/4-inch thick rounds.
In a large mixing bowl, whisk together the olive oil, tamari, nutritional yeast, garlic powder, sea salt, and black pepper until a thick paste forms.
Add the tofu cubes, diced potatoes, and sliced carrots to the bowl, tossing gently with a spatula until every piece is thoroughly and evenly coated.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the pieces are not crowded to allow for maximum crispiness.
Roast in the center of the oven for 25 to 30 minutes, flipping the tofu and vegetables halfway through, until the edges are golden brown and the potatoes are tender.
Remove the sheet from the oven and immediately add the fresh baby spinach, tossing it with the hot roasted ingredients until the leaves are just slightly wilted.