Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Season the chicken breast evenly on both sides with sea salt, black pepper, and half of the fresh thyme.
Clean the cremini mushrooms with a damp cloth, quarter them, and place them in a small mixing bowl.
Mince the garlic cloves and whisk them into the melted ghee, then pour the mixture over the mushrooms and toss to coat.
Place the seasoned chicken breast on one side of the baking sheet and spread the garlic butter mushrooms on the other side.
Roast in the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the mushrooms are golden brown.
While the chicken roasts, steam the green beans for 5 to 7 minutes until tender-crisp, then finish with a squeeze of fresh lemon juice.
Let the chicken rest for 5 minutes before slicing and serving alongside the buttery mushrooms and bright green beans.