Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Dice the chicken breast into 1-inch cubes and slice the cremini mushrooms into thick pieces.
In a small bowl, melt the ghee and whisk in the minced garlic, fresh thyme, sea salt, and black pepper.
Place the chicken and mushrooms in a large mixing bowl, pour the garlic-ghee mixture over them, and toss until every piece is thoroughly coated.
Spread the chicken and mushrooms in a single layer on the prepared baking sheet.
Roast for 18-20 minutes, or until the chicken is cooked through and the mushrooms have developed a golden-brown color.
While the chicken roasts, warm the pre-cooked quinoa in a pan over medium heat, stirring in the baby spinach until it is just wilted.
Divide the quinoa and spinach mixture between plates and top with the roasted garlic chicken and mushrooms.
Finish the dish with a bright squeeze of fresh lemon juice before serving.