Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Slice the chicken breast into bite-sized pieces and halve the cremini mushrooms.
In a large mixing bowl, whisk together the melted ghee, minced garlic, sea salt, and black pepper.
Add the chicken pieces and mushrooms to the bowl, tossing thoroughly until every piece is coated in the garlic ghee.
Spread the mixture in a single layer on the prepared baking sheet, ensuring space between pieces for optimal browning.
Roast for 18-20 minutes, or until the chicken is cooked through and the mushrooms are tender and golden.
Place the fresh baby spinach into a serving bowl and top immediately with the hot roasted chicken and mushrooms to gently wilt the greens.
Finish the dish with a sprinkle of fresh parsley and a bright squeeze of lemon juice.