Preheat your oven to 400°F (200°C) and prepare a grill or grill pan over medium-high heat.
In a small bowl, whisk together the lemon juice, minced garlic, dried oregano, and half of the olive oil to create a zesty marinade.
Place the chicken breast in a shallow dish, coat thoroughly with half of the marinade, and let it sit for at least 10 minutes.
On a parchment-lined baking sheet, toss the sliced bell peppers, zucchini, and red onion with the remaining olive oil, sea salt, and black pepper.
Roast the vegetables in the oven for 15-20 minutes, or until they are tender and show slight caramelization.
While the vegetables roast, place the chicken on the hot grill and cook for 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the heat and allow it to rest for 5 minutes to lock in the juices before slicing.
Arrange the roasted vegetables on a plate, top with the sliced chicken, and drizzle with the remaining lemon-herb mixture.