Preheat the oven to 375°F (190°C).
In a large skillet, heat the coconut oil over medium heat. Sauté the onion until translucent, about 3-4 minutes.
Add the garlic and mushrooms, and cook until the mushrooms are tender and browned, about 5-6 minutes.
Stir in the riced cauliflower and cook for another 3-4 minutes until slightly softened.
Add the chopped spinach, dried parsley, dried thyme, salt, and ground turmeric. Mix well.
In a separate bowl, combine the coconut cream, bone broth, and coconut aminos. Mix well.
Add the drained tuna to the cauliflower mixture and stir to combine.
Pour the coconut cream mixture over the tuna and cauliflower, stirring until evenly distributed.
Transfer the mixture to a baking dish and spread evenly.
Bake for 25-30 minutes, or until the casserole is bubbling and the top is slightly golden.
Garnish with chopped fresh parsley before serving.