Preheat your oven to 425°F and line a large rimmed baking sheet with parchment paper.
Clean and slice the cremini mushrooms, then toss them in a bowl with half of the ghee (melted), the dried thyme, and a pinch of the sea salt.
Spread the mushrooms in a single layer on the baking sheet and roast for 20 minutes until they are golden brown and crispy.
While the mushrooms roast, season the chicken breast on both sides with the remaining sea salt and black pepper.
Heat a heavy-bottomed skillet over medium-high heat and sear the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the pan and let it rest for 5 minutes before slicing into strips.
In the same skillet, reduce heat to medium and add the remaining ghee and minced garlic, sautéing for 1 minute until fragrant.
Add the baby spinach to the skillet and stir until just wilted, then fold in the roasted crispy mushrooms and lemon juice.
Plate the sliced chicken and top generously with the garlic butter mushroom and spinach mixture.