Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Cut the chicken breast into bite-sized cubes and halve the cremini mushrooms.
In a large mixing bowl, combine the chicken, mushrooms, melted ghee, minced garlic, smoked paprika, sea salt, and black pepper.
Toss everything together until the chicken and mushrooms are thoroughly coated in the spiced garlic butter.
Spread the mixture in a single layer on the prepared baking sheet, ensuring enough space for the mushrooms to roast rather than steam.
Roast for 18 to 20 minutes, or until the chicken is cooked through and the mushrooms are golden and tender.
Remove from the oven and immediately add the baby spinach to the hot pan, tossing gently until the greens are just wilted.
Garnish with freshly chopped parsley and serve immediately.