Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Slice the zucchini into half-moons, chop the red bell pepper into bite-sized pieces, and thinly slice the red onion.
In a small bowl, whisk together 0.5 tbsp of olive oil, the minced garlic, dried oregano, and a pinch of salt and pepper.
Place the chicken breast in a shallow dish and coat with the lemon juice and the prepared herb marinade; let it sit for 10 minutes.
Toss the prepared vegetables on the baking sheet with the remaining 0.5 tbsp of olive oil and the remaining salt and pepper.
Roast the vegetables in the oven for 15-20 minutes until they are tender and slightly caramelized at the edges.
While the vegetables roast, heat a grill pan or cast-iron skillet over medium-high heat.
Grill the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F and the outside has beautiful char marks.
Remove the chicken from the heat and let it rest for 3 minutes before slicing.
Plate the roasted vegetables alongside the sliced chicken and drizzle any remaining pan juices over the top before serving.