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 about 2 minutes to get a good sear, then stir and cook for another 2-3 minutes until the steak is cooked through.
Return the cooked onions to the skillet and mix with the steak.
Divide the steak and onion mixture evenly among the 4 hoagie rolls.
Top each sandwich with 2 slices of provolone cheese.
Place the sandwiches in a preheated oven at 350°F (175°C) for 3-5 minutes or until the cheese is melted.
Remove from oven and serve immediately.