Preheat oven to 425 degrees.Combine all meatball mixture ingredients in food processor. Process for 2 minutes until well mixed. Scoop into small meatballs and bake on a rack for 10 minutes or until fully cooked.
Combine all tzatziki ingredients and stir until well mixed.
To serve: Place romaine leaf on plate and top with meatballs, onions,tomatoes, feta and tzatziki as desired.