Lamb Burger with Chunky Mint Tzatziki Recipe

Name: Lamb Burger with Chunky Mint Tzatziki Recipe
Ingredients: 2/3 cup Greek yogurt; 1/2 English cucumber, seeds scooped out, skin peeled off, and cut into chunky half moons; 1/4 cup roughly chopped mint leaves; 1 bunch roughly chopped chives (about 1/3 cup), divided; 3 tablespoons roughly chopped fresh oregano (divided); 3 medium cloves garlic, minced (about 1 tablespoon); 2 teaspoons fresh juice from 1 lemon; Kosher salt and freshly ground black pepper; 14 ounces ground lamb; A drizzle of olive oil; 2 warm pitas