Heat a large skillet over medium heat and add the ground beef, cooking until browned (6-8 minutes), breaking it apart while cooking.

Drain excess fat, then stir in the sliced mushrooms and sauté for another 4-5 minutes until softened.

Lower heat and mix in the shredded cheese, cooking for 2-3 minutes until it melts and binds with the beef and mushrooms.

In a bowl, combine yogurt, diced cucumber, minced garlic, lemon juice, and dill; stir well and refrigerate for at least 15 minutes.

Warm pita bread in a skillet for 1-2 minutes on each side, then fill with the beef and mushroom mixture and drizzle with tzatziki.

Serve warm with extra tzatziki on the side for dipping.