Preheat your oven to 400°F.
Season the chicken breast evenly with sea salt and black pepper.
Heat the olive oil in a large oven-safe skillet over medium-high heat.
Sear the chicken for 3 to 4 minutes on each side until a golden crust forms.
Remove the chicken from the skillet and set it aside on a plate.
In the same skillet, add the ghee and the cremini mushrooms.
Sauté the mushrooms for about 5 minutes until they release their moisture and turn deep brown.
Stir in the minced garlic and fresh thyme, cooking for 1 minute until fragrant.
Place the chicken back into the skillet and transfer the pan to the oven.
Roast for 10 to 12 minutes until the chicken is cooked through.
Remove from the oven and toss in the fresh baby spinach, stirring until just wilted.