Add the ground beef, egg, tomato, onion, oregano, breadcrumbs, salt, and pepper in a large bowl and mix together until well combined.
Form the beef mixture into 1-1 ½“ size balls.
Place the meatballs on a sheet pan and bake in the oven for 30 minutes, until the internal temperature reaches 160 degrees F or your preferred doneness.
In a small bowl, whisk together the Greek yogurt and lemon juice.
Add the dill and cucumber to the yogurt mixture and stir together.
Season with salt to taste.
Stuff each pita bread with meatballs and tomato slices. Drizzle the cucumber dressing on top before serving.