Preheat the oven to 425°F (220°C).
In a large bowl, combine zucchini, red bell pepper, yellow bell pepper, red onion, and cherry tomatoes.
Drizzle 1/2 tablespoon olive oil over the vegetables, then season with 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper. Toss well to coat evenly.
Spread the vegetables in a single layer on a baking sheet lined with parchment paper.
Roast the vegetables in the preheated oven for 20 minutes, stirring halfway through.
While the vegetables roast, pat the chicken breasts dry with paper towels.
Rub the chicken breasts with the remaining 1/2 tablespoon olive oil.
Season both sides of the chicken breasts with 1/2 teaspoon kosher salt, 1/4 teaspoon black pepper, garlic powder, and dried thyme.
Heat a large skillet over medium-high heat.
Add the chicken breasts to the hot skillet and cook for 5-6 minutes on one side without moving them, until golden brown.
Flip the chicken breasts and cook for another 5-6 minutes, or until the internal temperature reaches 165°F (74°C).
Remove the chicken from the skillet and let it rest for 5 minutes.
Remove the roasted vegetables from the oven and drizzle with balsamic vinegar. Toss gently to combine.
Slice the chicken breasts and serve alongside the roasted vegetables.