Preheat your oven to 400°F (200°C).
Slice the chicken breast into 1-inch cubes and clean the cremini mushrooms, cutting any large ones in half.
Mince the garlic cloves finely.
In a large oven-safe skillet, melt the ghee over medium-high heat.
Add the chicken cubes to the skillet and sear for 3-4 minutes until they develop a light golden crust.
Stir in the mushrooms, minced garlic, sea salt, black pepper, and dried thyme, coating everything in the ghee.
Transfer the skillet to the preheated oven and roast for 12 minutes until the mushrooms are tender and the chicken is cooked through.
Remove from the oven and immediately toss in the baby spinach, allowing the residual heat to wilt the leaves.
Drizzle with fresh lemon juice before serving to brighten the savory flavors.