Grilled Meatballs

Name: Grilled Meatballs
Ingredients: 4 cups plain yogurt; 3 cloves garlic, finely minced; 3 tablespoons olive oil; 1 tablespoon lemon juice, or to taste; 1/4 cup chopped fresh mint; Salt and freshly ground pepper; 1 pound red onions, thinly sliced; 1 tablespoon salt; 1/2 cup chopped fresh flat leaf parsley; 1 teaspoon ground coriander; 1/2 teaspoon ground turmeric; 2 pounds ground beef; 1 1/2 cups grated onion; 2 minced garlic cloves; 2 eggs, lightly beaten; 1 tablespoon chopped fresh thyme; 1 teaspoon freshly ground black pepper; 1/2 teaspoon salt, or to taste; Olive oil for brushing; 6 pita breads, warmed; Sliced tomatoes