Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Slice the cremini mushrooms and trim the ends of the haricots verts.
In a mixing bowl, toss the mushrooms and haricots verts with half of the olive oil, half of the sea salt, and half of the black pepper.
Spread the vegetables in a single layer on the prepared baking sheet and roast for 15-18 minutes until the mushrooms are tender and the beans are slightly blistered.
While the vegetables roast, season the chicken thighs evenly with the remaining sea salt, black pepper, dried thyme, and dried rosemary.
Heat the remaining olive oil in a cast-iron skillet over medium-high heat until shimmering.
Place the chicken thighs in the skillet and sear for 5-7 minutes per side until a golden-brown crust forms and the internal temperature reaches 165°F.
In the final minute of cooking, add the minced garlic to the skillet, tossing it with the chicken juices to infuse the meat.
Remove from heat and serve the chicken alongside the roasted vegetable medley immediately.