Add the cream cheese, smoked salmon, lemon zest, capers, horseradish and onion powder to a bowl. Mix well to combine. Form into a ball.
Add the green onions and the sesame seeds to a pie plate or shallow dish. Transfer the cheese ball to the pie plate and coat with the onion and sesame seeds until fully coated.
Wrap the ball in plastic wrap and chill for at least 1 hour up to 48 hours before serving.