Process spinach in a food processor (you can skip this, but it won’t look as nice) then add in eggs, egg whites, salt, pepper, oil and seltzer and pulse a few more times to combine.  Pour into a bowl and mix in matzo meal.  Cover and chill for at least 1 hour or overnight, the longer it sits the fluffier it will be.

Bring large pot of generously salted water to boil. Using wet hands shape matzo mixture into 16 balls; drop into boiling water. Reduce heat to low, cover pot, and simmer until tender, about 45 minutes. Using slotted spoon, transfer matzo balls to the soup.