Mix the meatball base. In a large bowl, combine the ground turkey, egg, breadcrumbs, onion, garlic, soy sauce, ginger, salt, and pepper. Stir gently with a fork or your hands until just combined. Don’t overmix or the meatballs will be tough.

Shape the meatballs. Using damp hands or a small scoop, form 18–22 golf ball–sized meatballs. Place them on a parchment-lined tray while you heat the pan.

Brown the meatballs. In a large nonstick skillet, heat the oil over medium heat. Add meatballs in a single layer, leaving space between them. Cook 6–8 minutes total, turning occasionally, until browned on most sides. They don’t need to be cooked through yet.

Remove and sauté vegetables (optional). Transfer meatballs to a plate. If using bell pepper and onion, add them to the same skillet with a splash of oil. Sauté 3–4 minutes until crisp-tender. Stir in pineapple chunks if using.

Make the sauce. In a bowl, whisk pineapple juice, ketchup, vinegar, brown sugar, soy sauce, cornstarch, water, garlic, and ginger until smooth. Pour into the skillet and bring to a gentle simmer, stirring, until the sauce thickens and turns glossy, about 2–3 minutes.

Finish cooking the meatballs. Return the meatballs (and any juices) to the skillet. Spoon sauce over them. Cover and simmer on low for 6–8 minutes, or until the centers reach 165°F (74°C).

Taste and adjust. If the sauce is too tangy, add a teaspoon of brown sugar. If it’s too sweet, add a splash of vinegar or soy sauce. Thin with a bit of water if it’s too thick.

Serve. Top with scallions and sesame seeds. Serve over rice or noodles, or set out as an appetizer with toothpicks and extra sauce on the side.