In a large mixing bowl, combine the ground beef, uncooked rice, minced onion, egg, salt, pepper, and garlic powder. Mix gently with your hands until just combined, about 1 minute.

Roll the mixture into meatballs about 1.5 inches in diameter, using about 2 tablespoons of mixture per meatball to make about 20 meatballs.

In a medium saucepan or Dutch oven, combine the tomato sauce, diced tomatoes with juices, beef broth, brown sugar, Worcestershire sauce, and Italian seasoning. Stir until blended.

Place the pan over medium heat and bring the sauce to a gentle simmer, about 3 to 5 minutes, stirring occasionally.

Carefully add the meatballs to the simmering sauce, spacing them evenly so they are mostly submerged.

Reduce heat to medium-low, cover, and let the meatballs braise gently for 30 to 35 minutes without stirring too frequently.

After 30 minutes, cut one meatball in half to check that the rice is fully cooked and tender. Continue simmering uncovered if the sauce is too thin.

Taste the sauce and adjust seasoning with salt, pepper, or a pinch of brown sugar or Worcestershire sauce as needed before serving.