Preheat your oven to 400°F and heat an outdoor grill or grill pan to medium-high heat.
Slice the zucchini into rounds, the bell pepper into strips, and roughly dice the red onion.
In a large bowl, toss the vegetables with 0.5 tbsp of olive oil, the dried oregano, and half of the sea salt and black pepper.
Spread the vegetables in a single layer on a parchment-lined baking sheet and roast for 20 minutes until tender and slightly caramelized.
While the vegetables roast, season the chicken breast with garlic powder, lemon juice, and the remaining sea salt and black pepper.
Brush the grill grates with the remaining 0.5 tbsp of olive oil to prevent sticking.
Grill the chicken for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and the juices run clear.
Remove the chicken from the grill and let it rest for 3 minutes before serving alongside the roasted vegetables.