Heat ghee in a large Dutch oven or stockpot over medium heat. Add the chopped onions and cook until translucent, about 5 minutes. Stir in minced garlic and cook just until fragrant, about 1 minute. Then, stir in all the spices except for paprika: cumin, salt, ginger, cayenne pepper, cinnamon and turmeric. Mix in with the onions and fry for about 2 minutes until fragrant.
Stir tomato sauce into the spiced onion mixture and bring to a boil, then reduce heat to low. Simmer the sauce for about 10 minutes. Then add in the coconut milk, paprika, and liquid stevia. Bring sauce back to a simmer and cook for about 10-15 minutes, stirring often.
Season raw diced chicken tenderloins with the curry powder and salt. Spray a thin layer of cooking spray to a nonstick pan and heat over medium heat. Add to the hot pan and sear chicken until lightly browned but still pink inside, about 3 minutes. Transfer chicken and any juices into the sauce, and simmer until no longer pink, about 30 minutes.