Mix the base. In a medium bowl, whisk together pineapple juice, ketchup, vinegar, brown sugar, soy sauce, Worcestershire (if using), garlic powder, onion powder, and red pepper flakes until smooth.

Create the slurry. In a small cup, stir cornstarch with cold water until lump-free. Set aside.

Warm the aromatics (optional). If using peppers and onions, heat the oil in a large skillet over medium-high. Sauté for 3–4 minutes until slightly tender but still crisp. If not using veggies, heat the oil and move to step 4.

Simmer the sauce. Pour the sauce base into the skillet. Bring it to a gentle simmer over medium heat, stirring often.

Thicken. Stir the slurry again, then slowly whisk it into the simmering sauce. Cook for 1–2 minutes until the sauce turns glossy and thick enough to coat a spoon.

Add meatballs. Add cooked meatballs to the pan, turning to coat. If using pineapple chunks, fold them in now. Simmer for 5–7 minutes to let flavors meld and warm through.

Taste and adjust. Balance is key. Add a splash more vinegar if you want extra tang, a teaspoon of sugar if you want sweeter, or a pinch of salt if it needs more pop.

Serve. Top with sliced scallions or sesame seeds if you like. Serve over rice, noodles, or as a party appetizer with toothpicks.