1. Preheat your oven to 350°F (175°C). Lightly grease a loaf pan or line it with parchment paper for easy removal.
2. In a large skillet, sauté the chopped onion, bell pepper, and garlic over medium heat until soft and fragrant, about 5 minutes. Let it cool slightly.
3. In a large bowl, combine the ground beef, ground pork, sautéed vegetables, breadcrumbs, egg, milk, Worcestershire sauce, salt, pepper, and oregano. Mix gently until just combined.
4. Transfer half of the meat mixture into the prepared loaf pan, pressing down to level it. Layer half of the provolone cheese slices over the meat.
5. Top with the remaining meat mixture, pressing to compact it. Finish with a layer of the remaining cheese slices on top.
6. In a small bowl, mix together the ketchup, brown sugar, and mustard. Spread this glaze over the top of the meatloaf.
7. Bake in the preheated oven for 1 hour, or until the internal temperature reaches 160°F (70°C). Let it rest for 10 minutes before slicing.

Remember, patience is key here. Allowing the meatloaf to rest lets all those wonderful juices settle back in, creating that melt-in-your-mouth experience we all love.