Preheat the oven to 375°F (190°C). Lightly grease a 9×13 inch casserole dish with olive oil.
Steam the broccoli florets until just tender, about 4-5 minutes. Drain and set aside.
In a medium skillet, heat 2 tablespoons olive oil over medium heat. Add the chopped onion and sauté until translucent, about 4 minutes.
Add the minced garlic to the skillet and cook for 1 minute until fragrant.
Sprinkle the arrowroot powder over the onions and garlic, stirring constantly for about 1 minute to cook out the raw flavor.
Slowly whisk in the coconut milk and chicken broth, stirring continuously to create a smooth sauce.
Add the Dijon mustard, sea salt, black pepper, smoked paprika, dried thyme, and dried oregano. Stir well and cook until the sauce thickens, about 3-4 minutes.
In a large mixing bowl, combine the cooked chicken, steamed broccoli, and the prepared sauce. Mix until everything is evenly coated.
Transfer the mixture into the prepared casserole dish and spread it evenly.
Sprinkle the toasted sliced almonds evenly over the top of the casserole.
Bake in the preheated oven for 25-30 minutes, until the casserole is bubbly and the top is lightly golden.
Remove from the oven and let it rest for 5 minutes before serving.