Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat.
Add the sliced onions and cook, stirring occasionally, until they are soft and caramelized, about 8 minutes. Remove onions from skillet and set aside.
Add the remaining 1 tablespoon of vegetable oil to the skillet and increase heat to high.
Add the thinly sliced ribeye steak to the skillet in a single layer. Season with salt and black pepper.
Cook the steak without stirring for 1-2 minutes to brown, then stir and continue cooking until the steak is cooked through, about 3-4 minutes total.
Return the cooked onions to the skillet with the steak and mix well.
Divide the steak and onion mixture evenly among the hoagie rolls.
Top each sandwich with 2 slices of provolone cheese.
Place the sandwiches on a baking sheet and broil in the oven for 2-3 minutes until the cheese is melted and bubbly.
Remove from oven and serve immediately.