Preheat oven to 230°C / 450°F.
In a large bowl, combine sweet potatoes with olive oil. Add salt, chili powder and paprika. Use your hands to mix, so all pieces are coated.
On a baking sheet, spread sweet potatoes out in a single layer. Bake in preheated oven for 15 to 25 minutes, flipping halfway through.
In a large skillet, heat olive oil over medium-high heat. Add onions, salt and black pepper. Cook, stirring occasionally, until onions are translucent, about 10 minutes. Transfer onions to a plate and set aside.
Wipe down skillet and heat olive oil over medium-high to high heat. In batches, add steak and sear until brown but not crisp, about 2 minutes per side. Just before removing from heat, add cooked onions back in and stir. Season with garlic powder, salt and black pepper.
On each bun, add two slices of provolone cheese. Place a quarter of meat and onion mixture on top of the cheese. Repeat for remaining sandwiches and serve with sweet potato fries.