Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Rinse the quinoa under cold water, then combine it with 0.5 cup of water in a small saucepan; bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes.
While the quinoa cooks, slice the chicken breast into 1-inch bite-sized pieces and quarter the cremini mushrooms.
In a small bowl, melt the ghee and whisk in the minced garlic, chopped fresh thyme, sea salt, and black pepper.
Place the chicken and mushrooms on the prepared baking sheet and drizzle with the garlic-ghee mixture, tossing thoroughly to coat every piece.
Spread the mixture into a single layer and roast in the oven for 18 to 20 minutes until the chicken is cooked through and the mushrooms are golden and tender.
Remove from the oven, drizzle with fresh lemon juice, and serve immediately over the bed of fluffy cooked quinoa.