In a bowl, combine the chicken and yogurt. Let it marinate for at least 30 minutes (or up to overnight in your fridge for maximum flavor).
Heat vegetable oil in a large skillet over medium heat. Once hot, add the chopped onion and sauté until golden.
Add the garlic and ginger, cooking for another minute until fragrant. Then stir in the garam masala, cumin, turmeric, and chili powder, cooking for 2 more minutes.
Mix in the diced tomatoes and allow them to simmer for about 10 minutes, giving the sauce a nice base.
Add the marinated chicken to the skillet, stirring well to coat the chicken in the spices. Cook until the chicken is browned and cooked through, about 10-15 minutes.
Once the chicken is cooked, pour in the heavy cream, stir well, and let it simmer for a few more minutes until the sauce thickens slightly.
Season with salt and pepper to taste, then garnish with fresh coriander.
Serve hot with rice or naan, and enjoy your scrumptious Chicken Tikka Masala!