Combine ground beef, breadcrumbs, eggs, Parmesan, parsley, minced garlic, salt, pepper, and onion powder in a large bowl. Mix gently with your hands until just combined—overworking creates dense, tough meatballs instead of tender, flavorful ones.

Fold diced onion into the mixture and shape into approximately 24 meatballs, each about 1.5 inches in diameter. Uniform sizing ensures even cooking across your labor day grilled meatballs recipe, preventing some from drying while others remain undercooked.

Preheat your grill to medium heat and brush grates with olive oil to prevent sticking. Let it achieve consistent temperature for 8–10 minutes before adding meatballs.

Thread meatballs onto skewers or place directly on grill grates spaced one inch apart. Grill for 12–15 minutes, rotating every 3 minutes, until the exterior develops a caramelized crust and internal temperature reaches 160°F.

In a separate bowl, whisk together marinara sauce, beef broth, balsamic vinegar, and Italian seasoning. Pour this glaze over the grilled meatballs during the final 5 minutes of cooking, allowing flavors to meld beautifully.

Transfer cooked meatballs to a serving platter and let rest for 3 minutes before serving. This allows juices to redistribute, ensuring maximum tenderness in every bite of your heartwarming slow backyard cookout centerpiece.