- In a skillet pan, over medium heat, cook the diced onion with the oil until softened and light golden (about 5-7 minutes).  - 1 tablespoon olive oil, 1 yellow onion 
- Stir in the garlic and ginger, and cook for an additional 1 minute until very fragrant.  - 4 cloves garlic, 1 tablespoon grated fresh ginger or ginger paste 
- Transfer the onion mixture into a slow cooker.*I use a 5.5 QT slow cooker, but anything from 5-7 QT will work fine 
- Add the crushed tomatoes, heavy cream, tomato paste, garam masala, cumin, coriander, turmeric, smoked paprika, and salt to the slow cooker. Stir to combine.  - 1 can (28 oz) crushed tomatoes, 1 cup heavy cream, 2 tablespoons tomato paste, 2 tablespoons garam masala, 1 tablespoon ground cumin, 1 teaspoon ground coriander, 1 teaspoon turmeric, 1 teaspoon smoked paprika, 1 teaspoon kosher salt 
- Add the chicken pieces to the slow cooker and stir to coat them evenly in the tikka masala sauce.  - 2 pounds boneless, skinless chicken breasts or thighs 
- Cover the slow cooker with the lid and cook on LOW heat for 6-7 hours, or until the chicken is tender and cooked through (165 degrees F).  
- Taste the sauce and adjust the seasonings if needed.*The long cook time can sometimes mute the flavors, so I will usually add just a pinch of kosher salt at the end.  
- Serve over cooked white rice with naan bread on the side.