Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
In a mixing bowl, toss the sliced cremini mushrooms with the melted ghee, minced garlic, fresh thyme, sea salt, and black pepper until evenly coated.
Spread the mushrooms in a single layer on the prepared baking sheet and roast for 15 to 18 minutes until they are tender and golden brown.
While the mushrooms are roasting, heat the avocado oil in a cast-iron or stainless steel skillet over medium-high heat.
Pat the chicken breast dry and season lightly with an extra pinch of salt and pepper.
Place the chicken in the hot skillet and sear for 6 to 7 minutes per side, or until the internal temperature reaches 165°F.
Remove the chicken from the skillet and let it rest for 3 minutes to lock in the juices.
Serve the chicken breast on a plate topped with the roasted garlic butter mushrooms and any flavorful oils remaining on the baking sheet.