Place the onion, green pepper, and Italian dressing in a large skillet over medium heat; cook and stir until the onion has softened and turned translucent, about 5 minutes. Add the provolone, cream cheese, mayonnaise, salt, and pepper; stir until the cheese has melted. Remove the skillet from the heat and stir in the roast beef.
Pour the mixture into an oven proof baking dish and sprinkle with Parmesan cheese. Bake uncovered for 25 minutes or until hot and bubbly.