Preheat your oven to 400°F and prepare the vegetables by slicing the mushrooms and mincing the garlic.
Season the chicken breast evenly on both sides with the sea salt and black pepper.
Melt the ghee in a large oven-safe cast-iron skillet over medium-high heat.
Place the chicken in the skillet and sear for 3-4 minutes per side until a golden crust forms, then temporarily remove the chicken from the pan.
Add the sliced mushrooms to the same skillet and sauté for 5-6 minutes until they are tender and browned.
Stir in the minced garlic and fresh thyme, sautéing for just one minute until the aroma is released.
Return the chicken to the skillet, nestling it among the mushrooms, and transfer the pan to the oven.
Roast for 8-10 minutes or until the chicken reaches an internal temperature of 165°F.
Remove from the oven, toss in the baby spinach and lemon juice, and stir until the spinach is just wilted.
Serve the roasted chicken and mushrooms over the warm quinoa to soak up the golden garlic butter sauce.