Preheat the oven to 400°F (200°C).
Wash and dry the sweet potatoes. Cut each potato in half lengthwise and lightly score the flesh.
Arrange the sweet potato halves on a baking sheet and bake for approximately 35–40 minutes, or until the centers are fork-tender.
While the potatoes bake, melt the butter in a large sauté pan over medium-high heat.
Add the thinly sliced beef and burger seasoning. Sauté for 3–4 minutes, stirring occasionally.
Add the sliced mushrooms and chopped green onions. Continue cooking until the mushrooms have softened and the beef is fully cooked.
Sprinkle the flour evenly over the beef and mushrooms. Stir well and cook for 2–3 minutes to remove the raw flour taste.
Gradually pour in the beef broth while stirring. Continue cooking until the sauce begins to thicken and coat the beef and mushrooms.
Stir in 2 tablespoons of Parmesan cheese and cook briefly until the cheese melts into the sauce.
Remove the baked sweet potatoes from the oven. Divide the beef and mushroom mixture evenly among the four potato halves.
Sprinkle the remaining Parmesan over the Steak and Mushroom Stuffed Sweet Potatoes.
Return the stuffed potatoes to the oven and bake for another 5–10 minutes, until the filling is bubbling and the Parmesan has melted.
Serve warm with sour cream and additional chopped green onions, if desired.