Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Cut the chicken breast into 1-inch bite-sized pieces and halve or quarter the cremini mushrooms so they are a similar size to the chicken.
Mince the garlic cloves finely and strip the fresh thyme leaves from their woody stems.
In a small microwave-safe bowl, melt the ghee, then whisk in the minced garlic, sea salt, black pepper, and thyme leaves.
Place the chicken pieces and mushrooms in a large mixing bowl, pour the garlic ghee mixture over them, and toss thoroughly to ensure every piece is coated.
Spread the chicken and mushrooms onto the prepared baking sheet in a single, even layer to ensure they roast rather than steam.
Roast in the center of the oven for 18-20 minutes, or until the chicken is cooked through and the mushrooms have developed a golden-brown, caramelized exterior.
While the chicken roasts, warm your pre-cooked quinoa in a small pan or the microwave.
Serve the roasted chicken and mushrooms over the fluffy quinoa and finish with a bright drizzle of fresh lemon juice.