Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Slice the red potato into thin wedges and chop the carrots and Brussels sprouts into bite-sized pieces.
Place the chicken breast on one side of the baking sheet and arrange the chopped vegetables on the other side.
Drizzle the olive oil over both the chicken and the vegetables, ensuring even coverage.
Sprinkle the rosemary, thyme, garlic powder, sea salt, and black pepper over the entire tray.
Toss the vegetables with your hands or a spatula to coat them in the oil and spices, and flip the chicken once.
Roast in the oven for 20 to 25 minutes until the chicken reaches an internal temperature of 165°F and the potatoes are golden.
Remove from the oven and top the roasted vegetables with crushed walnuts for a satisfying crunch.
Serve the sliced chicken and vegetables immediately with a crisp pickle on the side.