Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Chop the zucchini, bell peppers, and red onion into bite-sized pieces.
Toss the vegetables on the baking sheet with half of the olive oil, sea salt, and black pepper.
Roast the vegetables for 20-25 minutes until they are tender and show slight charring.
While the vegetables roast, whisk together the remaining olive oil, lemon juice, minced garlic, and dried oregano in a small bowl.
Coat the chicken breast thoroughly in the marinade and let it sit for at least 10 minutes.
Heat a grill or grill pan over medium-high heat and lightly grease if necessary.
Grill the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F.
Remove the chicken from the heat and let it rest for 5 minutes before slicing.
Serve the sliced zesty chicken alongside the roasted vegetable medley.