In a bowl, combine Greek yogurt, finely grated cucumber, minced garlic, and chopped fresh dill. Stir until well mixed, then drizzle in olive oil. Set aside to let flavors meld.

Heat a large skillet over medium heat with olive oil. Add ground beef, breaking it apart with a spatula. Cook, stirring frequently, for about 5-7 minutes until browned. Then add sliced mushrooms, garlic powder, onion powder, salt, and pepper. Cook for an additional 5 minutes until mushrooms are tender.

Lower heat to medium-low, and add shredded cheese, stirring continuously until melted.

Remove from heat, gently open pita pockets, and spoon in the cheesy beef mixture. Top with tzatziki sauce.

Serve warm and enjoy your Cheesy Beef and Mushroom Pita Pockets!