Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Clean the cremini mushrooms with a damp cloth, quarter them, and finely mince the fresh garlic cloves.
In a small glass bowl, melt the ghee and whisk in the minced garlic, smoked paprika, sea salt, and black pepper until well combined.
Place the mushrooms in a bowl, drizzle with half of the garlic-ghee mixture, and toss to coat before spreading them in a single layer on the baking sheet.
Season the chicken breast lightly with salt and pepper, then sear in a preheated skillet over medium-high heat for 3 minutes per side until a golden crust forms.
Transfer the seared chicken to the baking sheet alongside the mushrooms and roast for 12 to 15 minutes, or until the internal temperature reaches 165°F.
In the last minute of cooking, toss the baby spinach in a bowl with the remaining garlic-ghee and lemon juice until the leaves are just beginning to soften.
Slice the chicken and serve it over the bed of wilted spinach, topped with the smoky roasted mushrooms and any remaining pan juices.