Mix diced chicken with marinade ingredients in a bowl. Cover and refrigerate for at least 15 minutes or overnight.
Heat 1 tablespoon of butter in a frying pan and cook the chicken for 8 minutes, flipping halfway. Remove from the pan.
Add remaining butter to the pan, sauté onions for 3 minutes, then add garlic, ginger, and spices. Cook for 1 more minute.
Stir in passata and tomato puree. Simmer on low heat for 10 minutes until thickened.
Add heavy cream and optional sweetener. Return chicken to the pan and cook for 5 minutes until heated through.
Serve warm with your choice of low-carb sides.