Tandoori Style Chicken Burgers with Cumin Yogurt Sauce

Name: Tandoori-Style Chicken Burgers with Cumin Yogurt Sauce
Ingredients: 1 1/2 lbs. (4 to 5) boneless skinless chicken thighs, cut into rough chunks; 4 scallions thinly sliced; 3 tablespoons chopped fresh ginger (from a peeled 2-inch piece); 2 tablespoons freshly squeezed lemon juice (from 1 lemon); 1 tablespoon paprika; 2 teaspoons ground cumin; 1/2 teaspoon ground cardamom; 1/4 teaspoon cayenne pepper; Coarse salt and ground pepper; Vegetable oil for grates; 4 (6-inch) whole-wheat pitas; 1 cucumber (8 ounces) halved lengthwise and thinly sliced on the diagonal; 1/2 cup fresh cilantro sprigs; Cumin yogurt sauce; Watermelon slices (optional)