1. 1. Preheat the oven to 375°F (190°C).

2. 2. In a skillet, cook the diced onion in butter until softened.

3. 3. Add the boneless skinless chicken breast halves to the skillet and cook until browned on both sides.

4. 4. Pour in the heavy whipping cream and canned coconut milk. Stir well to combine.

5. 5. Transfer the chicken mixture to a baking dish.

6. 6. In a bowl, mix together chopped walnuts, cheddar cheese, and shredded mozzarella. Sprinkle this mixture over the chicken in the baking dish.

7. 7. Bake in the preheated oven for 25-30 minutes or until the chicken is cooked through and the topping is golden brown.

8. 8. Serve hot and enjoy!