Preheat your oven to 400°F and set a grill or grill pan over medium-high heat.
Slice the zucchini, red bell pepper, and red onion into uniform bite-sized pieces.
Toss the vegetables with half of the olive oil, half of the sea salt, and half of the black pepper on a parchment-lined baking sheet.
Roast the vegetables for 18-20 minutes until they are tender and show golden caramelized edges.
While the vegetables roast, whisk together the remaining olive oil, lemon juice, minced garlic, and dried oregano in a small bowl.
Season the chicken breast with the remaining salt and pepper, then brush thoroughly with the lemon-garlic marinade.
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 to lock in the juices before slicing.
Plate the sliced chicken alongside the roasted vegetables and serve immediately.