Preheat your oven to 350°F (175°C). Gather your ingredients.

In a large skillet, heat olive oil over medium heat. Add green bell pepper, onion, and mushrooms and sauté for approximately 5 minutes.

Reduce heat and add thinly sliced roast beef. Season with garlic powder, salt, and pepper. Cook for another 3 to 5 minutes until heated through.

Lay provolone cheese slices side by side. Spoon the beef and vegetable mixture onto each slice.

Roll each provolone slice around the filling tightly and place seam-side down in a greased baking dish.

Bake in the preheated oven for about 10 minutes until the cheese melts and bubbles.

Remove from oven and let them rest for a few minutes before serving.