In a bowl, mix 1/2 cup plain yogurt, 1/2 tbsp minced garlic, 1/2 tbsp minced ginger, and 1 tbsp garam masala. Toss 1.5 lbs cubed chicken breasts in the marinade and let sit for 30 minutes.
Heat 1 tbsp oil in a large skillet over medium-high heat. Brown the marinated chicken for 5-6 minutes until cooked through. Remove and set aside.
In the same skillet, sauté 1 medium diced yellow onion, remaining 1/2 tbsp garlic, and 1/2 tbsp ginger until softened (about 4 minutes).
Stir in the remaining 1 tbsp garam masala and cook for 1 minute until fragrant.
Pour in 14 oz crushed tomatoes. Simmer for 10 minutes, allowing the sauce to thicken slightly.
Return the cooked chicken to the skillet. Stir in 1/2 cup heavy cream and simmer for 2 more minutes.
Garnish with 1/4 cup chopped fresh cilantro and serve warm over rice.