For the Meatloaf:

Preheat the oven to 375°F (190°C).
In a bowl, I combine ground beef, breadcrumbs, milk, chopped onion, chopped bell pepper, minced garlic, ketchup, Worcestershire sauce, dried oregano, salt, and black pepper.
I mix until well combined.
I transfer the mixture to a greased loaf pan, shaping it into a loaf.
I bake in the preheated oven for 45-50 minutes or until the meatloaf is cooked through.
For the Grilled Cheese:

Once the meatloaf is cooked, I let it cool slightly, then slice it into 1/2-inch thick slices.
I butter one side of each slice of bread.
On the non-buttered side, I place a slice of cheddar cheese, a slice of meatloaf, and a slice of mozzarella cheese.
I top it with another slice of bread, buttered side facing out.
I heat a skillet over medium heat and cook the sandwich on both sides until the bread is golden brown, and the cheese is melted.