Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Chop the bell pepper, zucchini, and red onion into uniform 1-inch pieces to ensure even roasting.
Place the vegetables on the baking sheet and toss with 0.5 tablespoon of olive oil, half of the sea salt, and half of the black pepper.
Roast the vegetables for 20-25 minutes, tossing halfway through, until they are tender and show slight caramelized edges.
While the vegetables roast, whisk together the remaining 0.5 tablespoon of olive oil, lemon juice, lemon zest, minced garlic, and dried oregano in a small bowl.
Season the chicken breast with the remaining salt and pepper, then brush both sides with half of the prepared lemon-garlic mixture.
Heat a grill pan or outdoor grill over medium-high heat and cook the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the heat and let it rest for 5 minutes before slicing it into strips.
Drizzle the remaining lemon-garlic glaze over the sliced chicken and serve immediately alongside the roasted vegetables.