Brown ground beef and onions in a large skillet over medium heat, crumbling as it cooks, until the beef is no longer pink and the onion is soft, about 5 minutes. Drain if necessary.

Add teriyaki sauce, water chestnuts, pineapple, garlic, and ginger to the skillet; stir to combine. Reduce heat and simmer for about 5 minutes.

Sprinkle with sesame seeds and sliced green onion. Serve hot.