Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
Clean the cremini mushrooms with a damp cloth and slice them into halves or quarters depending on size.
In a small bowl, melt the ghee and whisk in the minced garlic, chopped thyme, and chopped rosemary.
Place the mushrooms on one side of the baking sheet and toss with half of the garlic-herb ghee mixture, sea salt, and black pepper.
Season the chicken breast with the remaining salt and pepper. Heat an oven-safe skillet over medium-high heat and sear the chicken for 2 minutes per side until golden.
Transfer the chicken to the other side of the baking sheet (or leave in the skillet if large enough) and brush with the remaining garlic-herb ghee.
Roast in the oven for 12-15 minutes, or until the chicken reaches an internal temperature of 165°F and the mushrooms are tender and browned.
Place the fresh baby spinach on a plate, top with the roasted chicken and mushrooms, and drizzle with fresh lemon juice before serving.