Creating Keto Garlic Mushroom Chicken Casserole is simple if you follow these easy steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Sauté Chicken: In a large skillet, heat olive oil over medium-high heat. Add the chicken breasts and cook until browned on both sides, about 5-7 minutes per side. Remove from heat and set aside.
3. Cook Mushrooms and Garlic: In the same skillet, add sliced mushrooms and sauté for about 3-4 minutes until they are soft. Add minced garlic and cook for an additional minute until fragrant.
4. Prepare Sauce: Lower the heat and pour in the heavy cream. Stir in dried thyme, onion powder, salt, and black pepper. Allow the mixture to simmer for 3-4 minutes to thicken slightly.
5. Combine Chicken and Sauce: Place the browned chicken breasts back into the skillet and spoon the mushroom and cream mixture over the top. Sprinkle shredded mozzarella cheese evenly over the chicken.
6. Bake: Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through and the cheese is bubbly and golden.
7. Garnish: Remove from the oven and let it rest for a few minutes. Garnish with fresh parsley if desired.

These straightforward steps will guide you to create this incredible casserole that is sure to impress.