In a saucepan, combine brown sugar, white vinegar, ketchup, soy sauce, pineapple juice, and Chinese five spice powder. Simmer for 5 minutes, then mix in the cornflour mixture and cook until thickened, about 2 minutes. Set aside.

Heat vegetable oil in a large wok or pan over high heat. Add the mini meatballs and cook for 4-5 minutes until they are nearly cooked through and golden on the outside.

Toss in the sliced onion and red capsicum. Stir-fry for about 3 minutes, allowing them to soften and take on a bit of color.

Add the diced fresh pineapple and the prepared sauce to the pan. Stir-fry everything together until it's heated through and well mixed, ensuring the meatballs are coated in the sauce.

Finally, toss in the chopped spring onions after removing from heat. Serve immediately over fluffy steamed rice.