Greek Tuna Pita Pockets

Name: Greek Tuna Pita Pockets
Ingredients: 4 (2.6-ounce) pouches tuna, such as Tuna Creations Lemon Pepper; 1/3 Cup diced celery; 1/3 Cup chopped green bell pepper; 1/4 Cup diced red onion; 1/4 Cup pitted Kalamata olives, sliced; 1/4 Cup crumbled Feta cheese; 1/4 Cup plain, fat-free Greek yogurt; 1 Tablespoon extra-virgin olive oil; 4 Pita bread, top third of each sliced off; 4 Lettuce leaves; 1 Medium tomato, cored and cut into 8 slices; 1 Medium cucumber, cut into 16 slices