In a medium bowl, combine 1/4 cup yogurt, 1/2 tsp. garam masala, turmeric, 1/2 tsp. salt and pepper; stir in chicken until coated set aside. In a Dutch oven or 4 or 5-qt. saucepan heat 2 Tbsp. oil over medium heat. Add onion and a few pinches of salt; cook about 5 minutes until the onion softens and begins to turn golden brown in places. Stir in garlic, ginger, paprika, coriander, cumin and remaining 1 tsp. garam masala. Stir in tomato paste; cook about 45 seconds until darkened to brick red. Pour in the tomato sauce and 1 1/2 cups water; bring to a simmer. Lower heat to low and cook about 15 minutes until onion is completely soft and the sauce has thickened. Stir in remaining 1/2 cup yogurt and taste. Season with salt and pepper, as needed. Keep warm. Arrange an oven rack 6 inches from the broiler and preheat the broiler. Line a rimmed baking sheet with aluminum foil and add chicken in one layer. Brush the tops of chicken with remaining 1 Tbsp. oil. and season with salt. Broil about 5 minutes until chicken is cooked through (165°F internal temperature) and browned in places. Bring sauce to a simmer and stir in chicken. Serve immediately over basmati rice and garnish with cilantro. Serve lemon wedges and naan on the side, if desired.