Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Clean the cremini mushrooms and slice them into halves or quarters if they are large.
Cut the chicken breast into one-inch cubes to ensure even cooking.
In a large mixing bowl, whisk together the melted ghee, minced garlic, dried thyme, sea salt, and black pepper.
Add the chicken and mushrooms to the bowl and toss thoroughly until every piece is coated in the garlic-herb mixture.
Spread the mixture in a single layer on the prepared baking sheet, ensuring space between pieces for roasting.
Roast in the oven for 18 to 20 minutes until the chicken reaches an internal temperature of 165°F and the mushrooms are browned.
Remove from the oven and immediately stir in the fresh baby spinach, allowing the residual heat to wilt the leaves.
Garnish with freshly chopped parsley and serve warm.