In a medium bowl, combine all ingredients for Tzatziki sauce until thoroughly mixed. Sauce may be made up to 2 hours in advance. Cover and refrigerate until serving.
Cook Gorton's Grilled Salmon Fillets according to package instructions. Slice cooked fish into bite size, set aside.
Warm pitas in microwave oven. Place one pita on a plate and spread 1/2 cup of the lettuce and sliced salmon on top. Sprinkle each of a little chopped tomato, onion, Feta cheese and olives. Spoon about 3 Tbsp of the tzatziki sauce and fold in edges of pita.
Wrap sandwich in parchment paper for serving. Repeat with remaining pitas. Serve immediately.