Hawaiian Beef Casserole

2 tablespoons cooking oil

1 onion, chopped

1 pound ground beef

1 (19 ounce) can kidney beans with liquid

1 (19 ounce) can pineapple chunks with juice

1 cup ketchup

½ cup brown sugar

1 tablespoon cornstarch

2 teaspoons ground mustard

1 teaspoon salt

Preheat an oven to 350 degrees F (175 degrees C).

Heat the oil in a skillet over medium heat; cook the onion in the hot oil until softened, about 5 minutes. Crumble the ground beef into the skillet and cook and stir until completely browned, 5 to 7 minutes. Drain.

Stir the kidney beans with liquid, pineapple with juice, ketchup, brown sugar, cornstarch, mustard, and salt together in a large bowl. Add the ground beef and onions to the mixture and stir to coat. Pour into a large casserole dish.

Bake in the preheated oven until completely heated through, about 45 minutes.