Preheat your oven to 400°F (200°C) and line a baking sheet with parchment. Scrub the sweet potatoes clean and pierce them several times with a fork. Roast for 30-35 minutes until fork-tender.

While the sweet potatoes roast, heat 1 tablespoon of olive oil in a skillet over medium heat. Add minced garlic and sauté for 1 minute until fragrant. Add sliced mushrooms and cook for 5-7 minutes until golden brown. Add fresh spinach and cook until wilted, seasoning with salt, pepper, and nutmeg if desired.

In a mixing bowl, combine the sautéed mushroom and spinach mixture with ricotta cheese and mozzarella cheese if using. Mix until well combined.

Once the sweet potatoes are cool enough to handle, slice them open lengthwise and mash the insides with a fork. Spoon the filling into each sweet potato, packing it in generously.

Return the stuffed sweet potatoes to the oven and bake for an additional 10 minutes. Let cool slightly before serving warm.