Preheat the oven to 425°F (220°C).
In a large bowl, toss zucchini, red bell pepper, yellow bell pepper, and red onion with 1 tablespoon olive oil, 1/2 teaspoon sea salt, and 1/4 teaspoon black pepper. Spread the vegetables evenly on a baking sheet and roast in the oven for 20-25 minutes, stirring halfway through, until tender and slightly caramelized.
While the vegetables roast, prepare the chicken breasts. Pat chicken dry with paper towels. In a small bowl, mix garlic powder, smoked paprika, 1/2 teaspoon sea salt, and 1/4 teaspoon black pepper. Rub this spice mixture evenly over both sides of each chicken breast.
Heat 1 tablespoon olive oil in a large skillet over medium-high heat. When the oil is hot, add the chicken breasts and cook for 5-6 minutes on each side or until the internal temperature reaches 165°F (74°C) and the chicken is golden brown. Remove from heat and let rest for 5 minutes.
In a medium bowl, whisk together lemon juice, Dijon mustard, avocado oil, and 1/4 teaspoon sea salt to make the dressing.
In a large bowl, combine baby spinach, chopped parsley, and chopped cilantro. Pour the dressing over the salad and toss to combine.
To serve, plate one chicken breast with a portion of roasted vegetables and a side of the fresh herb salad.