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 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 well to coat every piece.
Spread the mixture into a single layer, ensuring there is space between the items so they roast rather than steam.
Roast for 18-20 minutes, or until the chicken is cooked through and the mushrooms are tender and beautifully browned.
Remove from the oven, drizzle with fresh lemon juice, and garnish with chopped parsley before serving warm.