Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the Brussels sprouts and cut them in half; slice the carrots into rounds and the red onion into thick wedges.
Place the vegetables on the baking sheet and toss with 0.5 tablespoons of avocado oil, half of the sea salt, and half of the black pepper.
Roast the vegetables for 20 to 25 minutes, tossing halfway through, until they are tender and the edges are beautifully caramelized.
While the vegetables roast, season the chicken breast evenly on both sides with the garlic powder, dried thyme, and the remaining salt and pepper.
Heat the remaining 0.5 tablespoons of avocado oil in a cast-iron or heavy-bottomed skillet over medium-high heat.
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 5 minutes to lock in the juices before slicing.
Serve the pan-seared chicken alongside the roasted vegetables for a clean, nutrient-dense meal.