Chicken Samosas with Cilantro Yogurt Dip

Name: Chicken Samosas with Cilantro-Yogurt Dip
Ingredients: 1 cup diced onion; 1 cup fresh cilantro leaves; 1 pound boneless, skinless chicken breasts, finely minced; 1 tablespoon fresh lemon juice; 1 tablespoon minced garlic; 1 tablespoon peeled and minced fresh ginger; 1 tablespoon tamarind paste; 1 teaspoon sugar, plus more to taste; 1½ tablespoons whole cumin seeds; 2 tablespoons grape seed, corn, or other neutral oil, plus more for deep frying; 2 tablespoons whole coriander seeds, finely ground; Four 8 inch square spring roll wrappers; Salt and freshly ground black pepper; ½ cup diced tomatoes; ½ teaspoon cayenne pepper; ½ teaspoon turmeric powder; ¾ cup plain whole milk yogurt