Preheat your oven to 375°F.
Cook broccoli in the microwave for 3 minutes.
Spread the chicken and broccoli evenly in a greased casserole dish.
In a saucepan over medium heat, add olive oil and minced garlic. Sauté until fragrant.
Add almond milk (or heavy cream), chicken broth, Dijon mustard, onion powder, dried thyme, salt, and pepper to the saucepan. Stir to combine.
Mix in almond flour until well combined.
Bring the sauce to a simmer and cook for a few minutes until it starts to thicken.
Remove the sauce from heat and stir in a half cup of the cheddar cheese and half of the Parmesan cheese until melted.
Pour the sauce evenly over the chicken and broccoli in the casserole dish.
Sprinkle the remaining cheddar and Parmesan cheese on top.
Bake in the preheated oven for about 18-20 minutes or until the cheese is melted and bubbly, and the casserole is heated through.
Allow the casserole to cool for a few minutes before serving.