Make the meatballs: Mix ground beef, ginger, garlic powder, and black pepper together in a large bowl until well combined. Shape into 1 1/2-inch balls.

Sauté meatballs in a large skillet over medium-high heat until browned, about 10 minutes.

While the meatballs are cooking, prepare the sauce: Pour pineapple juice into a liquid measuring cup, and reserve pineapple chunks; add enough water to pineapple juice to make 1 cup. Mix brown sugar and cornstarch in a small bowl.

Transfer meatballs to a plate, reserving the pan drippings. Add pineapple juice and brown sugar mixtures to the warm pan drippings. Stir in vinegar and soy sauce and bring to a boil. Cook until sauce thickens, 2 to 3 minutes.

Return meatballs to the skillet; add pineapple chunks, and green pepper. Simmer until meatballs are no longer pink inside, about 10 minutes. An instant-read thermometer inserted into the center should read at least 160 degrees F (71 degrees C).