Preheat the oven to 400°F(200°C). Line a baking sheet with parchment paper.
Combine the lamb, breadcrumbs, onion, garlic, parsley, mint, oregano, salt and pepper in a bowl. Mix well.
Form the mixture into 12 lightly-packed meatballs.
Spread the meatballs out on the baking sheet and bake for 18 minutes.
Mix all of the tzatziki ingredients in a bowl and chill until ready to serve.
Warm the pita rounds on a tray in the oven or in the microwave, until soft and warm.
To serve, place a meatball on each pita. Spoon on some tzatziki, and garnish with herbs.