Heat the vegetable oil in a large pan over high heat. Add the onion and cook for 10 minutes, until translucent and the edges start to brown.
Push the onion to one side of the pan and add the red and green bell peppers to the pan. Season with 2 teaspoons of salt, 1 teaspoon of garlic powder, and 1 teaspoon of pepper, and cook until the peppers soften, about 5 minutes. Remove from the pan and set aside.
Place the steak on the cutting board, and cover with a piece of plastic wrap. Pound with a meat mallet or rolling pin to about ½-inch (1 ¼ cm) thick.
Remove the plastic wrap and season the steak on both sides with 1 tablespoon of salt and 1 tablespoon of pepper.
Line 7 slices of Provolone cheese along the bottom edge of the steak. Place the sautéed vegetables on top.
Starting from the bottom, roll up the steak, encasing the cheese and vegetables inside.
Top with the remaining 7 slices of Provolone and secure with skewers or toothpicks.
Transfer the steak roll to a baking sheet and bake for 30 minutes, until cheese is melty and the steak is cooked through to your preference.
Rest for 10 minutes before slicing between the skewers and serving.