Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large bowl, combine the olive oil, garlic powder, onion powder, dried thyme, salt, and black pepper. Mix well.
Add the sweet potato slices to the bowl and toss until they are evenly coated with the oil and seasoning mixture.
Stack the sweet potato slices in groups of 4-5 and place them upright on the prepared baking sheet. Repeat until all slices are stacked.
Sprinkle the grated Parmesan cheese generously over the stacked sweet potatoes.
Bake in the preheated oven for 25-30 minutes, or until the sweet potatoes are tender and the cheese is golden and crispy.
Remove from the oven and let cool for a few minutes before serving. Garnish with fresh thyme leaves if desired.
