Preheat the oven to 400℉ and line a baking sheet with parchment paper.

In a medium bowl, mix together the avocado oil mayonnaise, drained and chopped pepperoncini, pepperoncini juice, red wine vinegar, minced garlic, kosher salt, and black pepper. Set aside in the fridge.

Pat the flank steak dry and slice it thinly against the grain, cutting longer pieces in half. In a medium bowl, toss the sliced steak with arrowroot starch, kosher salt, garlic powder, and black pepper.

Heat a large skillet over medium-high heat. Add the steak in a single layer and sear until golden brown, about 3 minutes. Flip and cook for an additional 1 to 2 minutes. Transfer to a plate and set aside. Repeat with remaining steak if necessary.

In the same skillet, add remaining avocado oil (if needed) and heat. Add the sliced onions and peppers, tossing to combine, and sauté until onions are golden brown and peppers are soft, about 5 to 7 minutes.

In a small bowl, mix together the Dijon mustard, coconut aminos, and fish sauce.

Reduce heat to medium. Add the cooked steak and its juices back to the skillet with the onions and peppers. Pour the coconut amino mixture over the top and toss to combine. Simmer until the sauce thickens, about 3 to 4 minutes, then set aside.

Place the halved rolls on the prepared sheet pan with the tops facing up. Brush the tops with melted butter and then flip, placing them butter side down. Spread the pepperoncini mixture on the rolls.

Layer 4 slices of provolone cheese on each roll half. Transfer to the oven and bake for 7 to 10 minutes until the rolls are golden and cheese is melted.

Top the bottom half of the rolls with the steak and veggie mixture, pressing down gently to adhere. Place the top half back over the meat and press gently to secure. Cut into 12 pieces and serve with toothpicks and an extra pepperoncini if desired.