Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Clean the cremini mushrooms with a damp cloth and halve any large ones so they are uniform in size.
Slice the chicken breast into 1-inch bite-sized pieces to ensure even cooking with the vegetables.
In a small bowl, whisk together the melted ghee, minced garlic, chopped thyme, chopped rosemary, sea salt, and black pepper.
Place the chicken and mushrooms on the prepared baking sheet and pour the garlic-herb ghee mixture over them, tossing well to coat every piece.
Spread the mixture into a single layer, ensuring the chicken and mushrooms aren't overcrowded so they roast rather than steam.
Roast in the oven for 18 to 20 minutes, or until the chicken is cooked through and the mushrooms are tender and golden brown.
Remove from the oven and immediately drizzle with fresh lemon juice to brighten the savory flavors before serving.