Preparation:
Take a bowl and add lemon juice, olive oil, capers, oregano, garlic powder, and pepper powder. Mix them well. Add tuna, tomatoes, red onions, olives, and cheese. Toss them to coat well. Refrigerate for 1 hour. Next, cut the pita bread in halves and line it with spinach. Place the tuna salad mixture into the 'pockets' of the bread and serve it with some tomato ketchup.