Heat a tablespoon of coconut oil in a non-stick skillet over medium-high heat. Add the diced yellow onion and sauté for about 5 minutes until it’s soft and translucent. Then, stir in the minced ginger, garlic, curry powder, garam masala, chili powder, salt, and tomato paste. Cook for an additional 30 seconds until fragrant.

Transfer the sautéed mixture into your slow cooker. Layer the boneless skinless chicken breasts on top, ensuring they're evenly spaced. Next, add the cauliflower florets if using, followed by the tomato sauce. Gently stir the mixture together.

Cut the unsalted butter into small pieces and scatter them over the top of your chicken and sauce mixture. Cover the slow cooker with its lid to trap the heat.

Cook your Slow Cooker Butter Chicken on high for 1.5 to 2.5 hours or on low for 4 to 6 hours until the chicken reaches an internal temperature of 165°F.

Check if the cauliflower is tender by inserting a fork. If it needs more time, stir gently and continue cooking on high for an additional 30 minutes to 1 hour.

Allow the dish to cool briefly, then cut the chicken into bite-sized pieces and return it to the slow cooker. Stir in the half-and-half or full-fat coconut milk.

Add the plain Greek yogurt, ensuring it has cooled slightly to avoid curdling. Stir well to combine for a creamy texture.

Serve warm over rice or with naan bread, and garnish with chopped cilantro.