Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
Arrange sweet potato slices on the sheet, drizzle with avocado oil, and sprinkle with 2 tbsp nutritional yeast, salt, and black pepper.Roast for 20–25 minutes, flipping halfway, until tender and slightly golden. While the sweet potatoes bake, heat 1 tsp avocado oil in a pan over medium heat.
Stir in chopped spinach and cook for 2–3 minutes until wilted.
Remove from heat and mix in the remaining 1 tbsp nutritional yeast and lemon juice (if using).
Once the sweet potato slices are done, spoon the spinach mixture onto each round. Return to the oven for an additional 3–5 minutes to let the flavours meld