Preheat oven to 450°F.
Place the hoagie rolls face down on a parchment lined baking sheet. Spread out julienned purple sweet potatoes (cut to ¼ inch thickness) on another parchment lined baking sheet, and drizzle with olive oil, salt, and pepper. Toast the rolls for 5 minutes, and roast the sweet potato fries for 25 minutes. (Note that the thinner fries are cut, the crispier they will turn out.)
In a skillet, grill the peppers and onions in olive oil on medium high heat, about 5 minutes. When slightly charred and tender, remove and set aside.
Flip the hoagie rolls and layer meat and one slice of provolone on each sandwich. Bake for another 5-7 minutes until cheese is melted and bubbling, and the bun is toasted.
While sandwiches and fries are baking, prepare the au jus dip. In a small saucepan, whisk together beef broth, soy sauce, salt, garlic powder, and pepper. Heat over medium high heat, about 5 minutes, until warm.
Top the baked sandwiches with grilled peppers and onion. Serve with ½ cup au jus dip and a side of fries. Enjoy!