In a large bowl, combine ground beef, breadcrumbs, finely chopped onion, eggs, and garlic powder. Season with salt and pepper, ensuring all ingredients are well incorporated without overmixing. Form mixture into small, even meatballs, about 1 inch in diameter, and set them aside.

For the air fryer method, preheat your air fryer to 380°F (193°C). Arrange the meatballs in a single layer and cook for 10 minutes, shaking the basket halfway through. Alternatively, preheat your oven to 400°F (204°C), place the meatballs on a lined baking sheet, and bake for 20-25 minutes until golden brown.

While the meatballs are cooking, whisk together rice vinegar, brown sugar, chicken broth, ketchup, tomato paste, pineapple juice, and cornstarch in a medium bowl. Stir in a pinch of salt to taste and set aside.

In a large skillet, heat vegetable oil over medium-high heat. Add sliced bell peppers and onion, sautéing for about 1 minute until they soften. Then, add minced garlic, cooking for an additional 30 seconds until fragrant.

Carefully pour the sweet and sour sauce over the sautéed vegetables, stirring continuously until the sauce thickens and bubbles, about 2-3 minutes. Gently add cooked meatballs and pineapple chunks, tossing until well coated.

Remove the skillet from heat and serve the Sweet and Sour Meatballs hot over rice or noodles or as an appetizer.