In a large mixing bowl, combine the diced beef, chopped onion, canned diced tomatoes, canned beans, soy sauce, brown sugar, and pineapple chunks along with their reserved juice. Stir everything together to coat the beef evenly in the sweet and tangy marinade.

Transfer the mixture into a casserole dish and cover with a lid or foil. Bake in a preheated oven at 180°C (350°F) for approximately 1½ hours, or until the beef is fork-tender and the flavors have melded beautifully. Alternatively, cook on low in a slow cooker for 4 to 5 hours for a hands-off option.

To finish, create a slurry by mixing cornflour with a small amount of water, then stir it into the casserole to thicken the sauce. Let it bubble for a few minutes until the sauce reaches your desired consistency.

Serve hot with creamy mashed potatoes or a bed of fluffy rice for a comforting, hearty meal.