Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Slice the chicken breast into 1-inch bite-sized pieces and halve the cremini mushrooms, keeping them similar in size for even cooking.
In a large mixing bowl, whisk together the melted ghee, minced garlic, sea salt, black pepper, and fresh thyme leaves.
Add the chicken and mushrooms to the bowl, tossing thoroughly until every piece is well-coated in the aromatic garlic butter.
Spread the mixture in a single layer on the prepared baking sheet, ensuring there is enough space between pieces to allow for proper browning.
Roast in the center of the oven for 18-20 minutes, or until the chicken is cooked through and the mushrooms are golden and tender.
While the chicken and mushrooms roast, place the fresh baby spinach and warm cooked quinoa in a serving bowl as your base.
Top the greens and grain with the roasted chicken and mushrooms, drizzling with fresh lemon juice just before serving to brighten the flavors.