Preheat your oven to 350°F (175°C) and prepare the baking dish.

Heat 1 tablespoon of olive oil in a large skillet over medium heat until shimmering.

Add sliced green bell pepper, onion, and mushrooms to the skillet and sauté for about 5 minutes.

Add 1 pound of thinly sliced roast beef, garlic powder, salt, and pepper; cook for another 3 to 5 minutes.

Lay out 8 slices of provolone cheese and spoon a portion of the beef and vegetable mixture onto each slice.

Roll each slice of provolone tightly around the filling, tucking in the sides.

Place the roll-ups seam-side down in the prepared baking dish and bake for about 10 minutes until cheese is melted.

Let the roll-ups sit for a few minutes before serving.