Preheat your oven to 350°F (175°C).

In a skillet over medium heat, pour in a splash of olive oil. Add your diced green bell pepper, sliced onion, and mushrooms. Sauté for about 5 minutes until tender.

Introduce the thinly sliced roast beef, season with garlic powder, salt, and pepper, and cook for another 3–5 minutes.

Lay provolone cheese slices out on a flat surface and portion the beef and vegetable mixture onto each slice.

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

Bake for about 10 minutes, or until the provolone cheese is melted and bubbly.

Remove from oven and allow to rest for a few minutes before serving.