Preheat oven to 350F
Wash and scrub the sweet potatoes, pierce the skin several times with a fork, bake for approximately 1-hour until they can be easily pierced with a knife. Remove from the oven and let cool slightly while you sauté the mushrooms. (Microwaved baked sweet potatoes work just as well.)
Heat a covered skillet over medium-high heat, and olive oil and butter, add mushrooms, salt, and pepper, stir frequently
After 5 minutes, add the onions and garlic, continue until the mushrooms are brown and the onions are soft
Turn off the heat and add the spinach on top, cover and let the spinach gently steam
The sweet potatoes should be cool enough to handle, cut each potato in half lengthwise, using a spoon, gently scoop the flesh out of the potato, careful not to damage the skin
Add half of the parmesan cheese to the sweet potato flesh and give it a rough mash, add the mixture to the spinach mushroom mixture and combine well
Gently spoon the spinach mushroom mixture into the sweet potato skins and line them up on a sheet tray, sprinkle the remaining Parmesan cheese on top and return to the oven
Bake for approximately 15 minutes, until the topping is just turning brown and crispy
Garnish with fresh chopped parsley as garnish