Preheat your oven to 400°F and heat a grill or grill pan over medium-high heat.
On a large rimmed baking sheet, toss the broccoli, sliced bell peppers, and red onion with half of the olive oil, a pinch of salt, and a pinch of pepper.
Roast the vegetables in the oven for 15 to 20 minutes until they are tender and the edges are slightly caramelized.
While vegetables roast, rub the chicken breast with the remaining olive oil, garlic powder, oregano, salt, and pepper.
Place the chicken on the hot grill and cook for 6 to 7 minutes per side, or until the internal temperature reaches 165°F.
Remove the chicken from the grill and let it rest for 5 minutes to lock in the juices before slicing.
Plate the grilled chicken alongside the roasted vegetable medley and serve immediately.