Preheat your oven to 175°C (350°F) and grease a 23 x 33 cm (9x13 inch) baking dish with butter.

In a deep skillet, cook the ground beef over medium heat for about 7-10 minutes until browned. Drain excess grease.

Add the diced onion and green bell peppers to the skillet and cook for 5-8 minutes until the onion is translucent.

Stir in ketchup, mustard, Worcestershire sauce, and brown sugar, allowing to simmer for a minute. Season with salt and black pepper.

Gently fold in the undrained pork and beans into the mixture, ensuring all ingredients are well combined.

Pour the beef and bean mixture into the prepared baking dish, cover with aluminum foil, and bake for 45 minutes.

Let the casserole rest for 10 minutes before serving to thicken the sauce.