Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Clean the cremini mushrooms with a damp cloth and slice them into halves; dice the chicken breast into uniform 1-inch pieces.
In a small bowl, whisk together the melted ghee, minced garlic, fresh thyme, sea salt, and black pepper until well combined.
Place the chicken and mushrooms on the prepared baking sheet and pour the garlic-herb ghee over them, tossing until every piece is well coated.
Spread the mixture into a single layer, ensuring there is enough space between pieces so the mushrooms roast and brown rather than steam.
Roast for 18 to 20 minutes, or until the chicken is cooked through and the mushrooms have developed a golden-brown, caramelized crust.
Remove from the oven, squeeze the fresh lemon juice over the top, and sprinkle with the chopped fresh parsley.
Serve the roasted chicken and mushrooms immediately over the warm, fluffy cooked quinoa.