Step 1: Preheat your oven to 400°F (200°C). This ensures your meatballs will cook evenly and get that perfect golden-brown color.
Step 2: In a large mixing bowl, combine the lean ground beef, finely diced onion, Panko crumbs, milk, beaten egg, salt, black pepper, and ground ginger. Mix until just combined, being careful not to overmix.
Step 3: Using your hands, shape the mixture into meatballs about 1 inch in diameter. Place them on a baking sheet lined with parchment paper, ensuring they are spaced out evenly.
Step 4: Bake the meatballs in the preheated oven for 20-25 minutes, or until they are cooked through and browned on the outside.
Step 5: While the meatballs are baking, heat vegetable oil in a skillet over medium heat. In a bowl, mix together the cornstarch, brown sugar, reserved pineapple juice, water, vinegar, and soy sauce until smooth. Add finely diced green bell pepper and bring the mixture to a simmer, stirring occasionally.
Step 6: Once the meatballs are done baking, transfer them to the skillet with the sauce. Gently stir to coat the meatballs evenly. Let them simmer for an additional 5-10 minutes to allow the flavors to meld.
Step 7: Serve your Polynesian Meatballs over a bed of rice, if desired. Garnish with sliced green onions for a pop of color and extra flavor. Enjoy the taste of the tropics!