Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Clean the cremini mushrooms and slice them into thick halves or quarters if they are large.
Season the chicken breast evenly on both sides with the sea salt and black pepper.
In a small microwave-safe bowl, melt the ghee and whisk in the minced garlic and fresh thyme leaves.
Place the chicken breast and sliced mushrooms onto the prepared baking sheet, then drizzle the garlic-ghee mixture over everything, tossing the mushrooms to coat.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken is cooked through and the mushrooms are golden brown.
Remove the pan from the oven and transfer the chicken to a cutting board to rest for 5 minutes.
While the chicken rests, stir the plain Greek yogurt directly into the warm mushroom juices on the baking sheet until a smooth, creamy sauce forms.
Slice the chicken, return it to the pan to coat in the sauce, and garnish with freshly chopped parsley before serving.