1. Cook the beef mixture: Heat olive oil in a skillet over medium heat. Add the onion and cook until translucent. Stir in the garlic, then add the ground beef. Cook until the beef is browned.

2. Add mushrooms and spices: Stir in the diced mushrooms, smoked paprika, cumin, salt, and pepper. Cook until the mushrooms are tender and the liquid has mostly evaporated.

3. Make the tzatziki sauce: In a bowl, combine Greek yogurt, grated cucumber, garlic, lemon juice, dill, and a pinch of salt. Mix well and chill until ready to serve.

4. Assemble the pita pockets: Lightly warm the pita pockets to make them easy to open. Fill each one with the beef and mushroom mixture, then sprinkle in the shredded cheese.

5. Melt the cheese: Place the filled pita pockets on a baking sheet and bake at 375°F (190°C) for 5-7 minutes, or until the cheese is melted and bubbly.

6. Serve and enjoy: Serve the hot Cheesy Beef and Mushroom Pita Pockets with a generous dollop of tzatziki sauce on the side or spooned inside the pocket. Enjoy this delicious and satisfying meal!