Preheat the oven to 425°F (220°C).
In a large bowl, combine the carrots, zucchini, red bell pepper, and red onion with 1 tablespoon of olive oil, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Toss to coat evenly.
Spread the vegetables on a large baking sheet in a single layer. Roast in the preheated oven for 20-25 minutes until tender and slightly caramelized, stirring halfway through cooking.
While the vegetables roast, pat the chicken breasts dry with paper towels.
Season both sides of the chicken breasts with 1/2 teaspoon kosher salt, 1/4 teaspoon black pepper, garlic powder, and dried thyme.
Heat the remaining 1 tablespoon of olive oil in a large skillet over medium-high heat.
Add the chicken breasts to the skillet and cook for 5-7 minutes on each side, or until the internal temperature reaches 165°F (74°C) and the chicken is golden brown.
Remove the chicken from the skillet and let rest for 5 minutes.
Transfer the roasted vegetables to a serving platter. Slice the chicken breasts and arrange on top or alongside the vegetables.
Drizzle fresh lemon juice over the chicken and vegetables before serving.