Preheat the oven to 375°F (190°C).
Lightly grease a 9×13 inch casserole dish with olive oil.
Bring a large pot of salted water to a boil. Add the broccoli florets and blanch for 2 minutes until bright green and slightly tender. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add diced onion and cook for 4-5 minutes until softened.
Add minced garlic to the skillet and cook for 1 minute until fragrant.
In a small bowl, whisk together coconut milk, chicken broth, arrowroot starch, Dijon mustard, sea salt, black pepper, smoked paprika, dried thyme, onion powder, and garlic powder until smooth.
Pour the coconut milk mixture into the skillet with the onions and garlic. Stir continuously and cook for 3-4 minutes until the sauce thickens.
Add the cooked chicken and blanched broccoli to the skillet. Stir to combine and coat evenly with the sauce.
Transfer the mixture into the prepared casserole dish and spread evenly.
Bake uncovered for 25-30 minutes until the casserole is bubbly and slightly golden on top.
Remove from the oven and let it cool for 5 minutes.
Sprinkle chopped fresh parsley over the casserole before serving.