Preheat your oven to 400 degrees Fahrenheit (200 degrees Celsius). Pierce the sweet potatoes several times with a fork.
Bake the sweet potatoes directly on the oven rack for 45 to 60 minutes, or until they are soft when squeezed.
While the potatoes bake, heat the olive oil in a skillet over medium heat. Add the sliced mushrooms and cook until they release their liquid and brown, about 5 to 7 minutes.
Add the minced garlic to the skillet and cook for 1 minute until fragrant.
Add the spinach to the skillet in batches, stirring until it wilts completely. Remove the skillet from the heat.
In a small bowl, mix the softened cream cheese, Parmesan cheese, salt, and pepper.
Once the potatoes are cool enough to handle, slice them lengthwise down the center, opening them up without cutting all the way through. Fluff the inside flesh slightly with a fork.
Stir the cream cheese mixture into the mushroom and spinach mixture.
Spoon the creamy filling evenly into the opened sweet potatoes.
Top each stuffed potato with shredded mozzarella cheese.
Return the potatoes to the oven for 5 to 7 minutes, or until the cheese is melted and bubbly. Serve immediately.
Notes
For a tangier flavor, substitute goat cheese for the cream cheese.
You can add a pinch of dried thyme with the mushrooms for an earthy note.