In a medium bowl, mix the Greek yogurt, grated cucumber, lemon juice, dill, minced garlic, olive oil, salt, and pepper. Stir well and chill for 15 minutes to allow flavors to meld.

Heat the olive oil in a large skillet over medium heat. Add diced onions and minced garlic, sautéing them until fragrant and translucent—about 3-4 minutes.

Toss in the chopped mushrooms and cook until they are nicely browned and tender, stirring occasionally, which should take around 5-6 minutes.

Stir in the ground beef, breaking it apart with a spatula. Cook until browned, ensuring it’s no longer pink—about 5-7 minutes.

Sprinkle in paprika, cumin, salt, and pepper. Stir well to coat the beef mixture with the spices, and let it simmer for a couple of minutes to set the flavors.

Once the liquid has evaporated from the beef mixture, stir in the shredded cheese until it's melted and evenly distributed. Take off the heat.

While the beef is finishing up, warm your pita pockets in the microwave or on a skillet for about 1-2 minutes until they're soft and pliable.

Carefully open each pita pocket and generously fill them with the cheesy beef and mushroom filling.

Finish by drizzling a good amount of chilled tzatziki sauce inside each stuffed pita, then garnish with fresh herbs if desired.