Preheat your oven to 400°F (200°C) and line a sheet pan with parchment paper.
In a small bowl, whisk together olive oil, balsamic vinegar, garlic, thyme, salt, and pepper.
Place chicken thighs and mushrooms on the prepared sheet pan. Drizzle the olive oil mixture over everything, tossing to coat evenly.
Arrange the chicken skin-side up and spread the mushrooms around it in a single layer.
Roast in the preheated oven for 35-40 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Optionally, add cherry tomatoes or asparagus during the last 10 minutes of cooking.
Remove from the oven and let rest for 5 minutes before serving.