Brown hamburger with onion in a skillet over medium heat until the hamburger is cooked through and the onion is softened.

Preheat oven to 325°F (160°C).

In a large baking dish, combine the browned hamburger and onion mixture with pork and beans, brown sugar, mustard, and catsup.

Mix all ingredients thoroughly until well combined.

Bake in the preheated oven for 45 minutes, or until bubbly and heated through.

Season with a little salt and pepper to taste before serving.