Pat your chicken breast pieces dry and set them aside. Heat the vegetable oil in your skillet over medium-high heat. Add the finely chopped onion and sauté until translucent and soft, about 5 minutes.
Add the minced garlic and grated ginger to the skillet. Cook for about 1 minute until fragrant. Then stir in the garam masala, ground cumin, paprika, and turmeric. Toast the spices for about 30 seconds to release their aroma.
Add the chicken pieces to the skillet. Stir well to coat the chicken in the spices and onion mixture. Cook until the chicken is no longer pink on the outside, about 5-7 minutes.
Pour in the diced tomatoes with their juices and the coconut milk. Stir everything together, scraping the bottom of the pan to loosen any browned bits. Bring the mixture to a gentle simmer, then reduce the heat to low. Let it cook for 10-15 minutes until the chicken is fully cooked and the sauce has thickened slightly.
Taste the sauce and season with salt as needed. Sprinkle fresh cilantro over the top for a burst of color and freshness. Serve your Chicken Tikka Masala Skillet hot with fluffy rice or warm naan bread to soak up every bit of that delicious sauce.