Preheat your oven to 400°F (200°C) and heat a grill pan or outdoor grill over medium-high heat.
In a small bowl, whisk together 0.5 tbsp of olive oil, the lemon juice, minced garlic, dried oregano, and smoked paprika.
Coat the chicken breast thoroughly with the marinade and season with half of the sea salt and black pepper.
Slice the zucchini into rounds, the bell pepper into strips, and the red onion into wedges.
Toss the vegetables in a bowl with the remaining 0.5 tbsp of olive oil and the rest of the salt and pepper.
Spread the vegetables in a single layer on a parchment-lined baking sheet and roast for 18-20 minutes until tender and slightly charred.
While vegetables roast, grill the chicken for 6-7 minutes per side until it reaches an internal temperature of 165°F.
Allow the chicken to rest for 5 minutes to lock in the juices before slicing and serving with the roasted vegetables.