Preheat the oven to 400°F (200°C).
Cut the sweet potatoes in half lengthwise and score the cut sides lightly with a knife.
Place the sweet potatoes cut-side up on a baking sheet. Bake for 35–40 minutes, or until 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 are tender and the beef is fully cooked.
Sprinkle the flour evenly over the beef and mushroom mixture. Stir well and cook for 2–3 minutes to remove the raw flour taste.
Gradually pour in the beef broth, stirring constantly. Cook until the sauce thickens.
Stir in 2 tablespoons of Parmesan cheese and cook until melted and incorporated.
Divide the beef and mushroom mixture evenly among the four baked sweet potato halves. This filling is the heart of these Steak and Mushroom Stuffed Sweet Potatoes.
Sprinkle the remaining Parmesan over the tops.
Return the stuffed potatoes to the oven and bake for 5–10 minutes, or until the filling is bubbling and the cheese has melted.
Serve warm with sour cream.