In a large mixing bowl, combine the ground beef (and ground pork if using), breadcrumbs, green onions, eggs, garlic powder, salt, and pepper. Mix the ingredients together using hands until well combined.
Form the mixture into 40-gram meatballs, which should yield about 26 meatballs. Place the meatballs on a baking sheet or plate and cover with plastic wrap. Chill in the refrigerator for at least 30 minutes to overnight to firm up.
Preheat the grill to medium heat. Remove the meatballs from the refrigerator and thread them onto skewers along with the prepared pineapple and veggies, starting with pineapple, then adding a sweet pepper, red onion, and a meatball. Repeat this pattern until the skewer is 1/3 full, then repeat.
In a saucepan, combine ketchup, soy sauce, apricot jam, rice vinegar, honey, and hoisin or oyster sauce. Cook over medium heat, stirring occasionally, until the sauce is heated through, about 5-7 minutes. Remove from heat and set aside.
Grill the meatball skewers for about 8-10 minutes, turning them occasionally to ensure even cooking until cooked through. At the halfway point, brush the skewers generously with the sweet and sour sauce. Continue grilling for another 2-3 minutes to allow the sauce to caramelize slightly. Remove from grill and enjoy!