In a bowl, mix together the tuna, oil, vinegar, lemon juice, celery, onion, cucumber, olives, and tomatoes. Season with salt and pepper to taste. Be careful not to add too much lemon. Refrigerate until ready to serve.
Warm the pita on both sides in a nonstick pan on medium heat.
Spread the lettuce and tuna mixture on the pita. Fold in half and serve with chips and pickle.