Place the yogurt and juice of 1 lemon in a zip top bag.
Add the greek salad dressing if desired and mix together by squishing it around.
Unwrap and place your chicken breasts into the marinade and squish it around so it's all covered.
Place in the refrigerator for 6 to 24 hours.
Remove from the bag and grill until they reach an internal temp of 165 degrees.
Remove from the grill and let sit covered for 5 minutes
Mix together green onions, tomatoes, feta cheese, and greek salad dressing in a bowl.
Place chicken on a platter and top with the feta cheese mixture.