Brown the beef: In a large skillet over medium heat, cook the ground beef with the mushrooms, onion, and bell pepper until the beef is cooked through and the vegetables are softened. Season with kosher salt and fresh ground pepper.
Make it creamy: Stir in the Worcestershire sauce, granulated garlic, and granulated onion. Add the softened cream cheese and stir until fully melted and the mixture is creamy and well combined.
Assemble the sandwiches: Spoon the sloppy joe mixture onto the bottom halves of the buns. Top with provolone cheese, place the top buns on, then brush with melted butter and sprinkle with sesame seeds.
Warm and melt: Place the sandwiches on a parchment-lined baking sheet and bake until the cheese is melted and the buns are warmed through.