In a small bowl, whisk together the extra virgin olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper to create the marinade.
Slice the chicken breast into 1-inch strips and chop the zucchini, red bell pepper, and red onion into uniform bite-sized pieces.
Place the chicken and vegetables in a large bowl, pour the marinade over them, and toss until everything is evenly coated.
Preheat a grill or a large cast-iron grill pan over medium-high heat.
Arrange the chicken and vegetables on the grill in a single layer, working in batches if necessary to avoid crowding.
Grill for 5-6 minutes per side, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with visible char marks.
Remove from heat and let the chicken rest for 2 minutes before serving to ensure it stays juicy.