Preheat your oven to 400°F and line a baking sheet with parchment paper.
Clean the mushrooms with a damp cloth and halve any that are particularly large.
In a bowl, toss the mushrooms with the olive oil, minced garlic, fresh thyme, half the salt, and half the pepper.
Spread the mushrooms in a single layer on the baking sheet and roast for 18-20 minutes until they are tender and deeply browned.
While mushrooms roast, season the chicken breast with the remaining salt and pepper.
Heat the ghee in a medium skillet over medium-high heat until shimmering.
Place the chicken in the skillet and sear for 6-7 minutes per side until the exterior is golden and the internal temperature reaches 165°F.
Remove the chicken from the pan to rest for 3 minutes, then add the spinach to the warm skillet to wilt for 30 seconds.
Slice the chicken and serve it over the bed of wilted spinach.
Top the chicken with the hot roasted garlic mushrooms and a bright squeeze of lemon juice.