Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into 1-inch bite-sized pieces and halve the cremini mushrooms, ensuring they are similar in size for even roasting.
In a small bowl, whisk together the melted ghee, minced garlic, chopped thyme, and chopped rosemary until well combined.
Place the chicken and mushrooms on the prepared baking sheet, then drizzle the garlic-herb ghee over the top and season with sea salt and black pepper.
Toss everything thoroughly to ensure every piece is coated in the fragrant fat and aromatics, then spread them out in a single layer.
Roast in the oven for 18 to 22 minutes, tossing halfway through, until the chicken is cooked through and the mushrooms are golden and tender.
Remove from the oven, drizzle with the balsamic vinegar while still hot, and serve immediately for a savory, high-protein meal.