Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Cut the chicken breast into 1-inch bite-sized pieces and halve the cremini mushrooms.
In a large mixing bowl, combine the chicken, mushrooms, minced garlic, fresh thyme, and fresh rosemary.
Melt the ghee and pour it over the mixture, tossing thoroughly to ensure every piece is well-coated in the herb-fat mixture.
Season with sea salt and black pepper, then spread the contents in a single layer on the prepared baking sheet.
Roast for 18 to 20 minutes, or until the chicken is cooked through and the mushrooms are golden and tender.
Place the fresh baby spinach in a serving bowl and immediately top with the hot chicken and mushroom mixture to gently wilt the greens.
Finish the dish with a squeeze of fresh lemon juice to brighten the earthy flavors before serving.