Set your sous vide immersion circulator to 165°F (74°C) in a large container of water.
Season the chicken thighs evenly on both sides with sea salt, black pepper, rosemary, and thyme.
Place the seasoned chicken thighs and the smashed garlic clove into a vacuum-seal bag and seal it tightly.
Submerge the bag in the water bath and cook for 1.5 hours to ensure the chicken is tender and fully cooked.
While the chicken is in the water bath, preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the sliced carrots and parsnips with olive oil and a pinch of salt, then spread them in a single layer on the baking sheet.
Roast the vegetables for 25-30 minutes, tossing halfway through, until they are tender and beautifully caramelized.
Once the chicken is done, remove it from the bag and pat it thoroughly dry with paper towels to ensure a good sear.
Heat the avocado oil in a cast-iron skillet over medium-high heat and sear the chicken for 1-2 minutes per side until a golden crust forms.
Serve the seared chicken thighs immediately alongside the roasted carrots and parsnips.