Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Chop the zucchini, red bell pepper, and red onion into uniform bite-sized pieces.
In a bowl, toss the vegetables with half of the olive oil, the balsamic vinegar, and a pinch of the sea salt and black pepper.
Spread the vegetables in a single layer on the prepared baking sheet and roast for 20-25 minutes until tender and slightly caramelized.
While the vegetables are roasting, season the chicken breast with the garlic powder, dried oregano, lemon juice, the remaining olive oil, and the rest of the sea salt and black pepper.
Heat a grill pan or outdoor grill 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 and beautiful grill marks appear.
Remove the chicken from the heat and let it rest for 5 minutes before slicing.
Serve the sliced grilled chicken alongside the warm roasted balsamic vegetables.