Preheat your oven to 425°F (220°C). Line a large, rimmed metal baking sheet with parchment paper for easy cleanup.
In a small bowl, whisk together the olive oil, fresh lemon juice, lemon zest, minced garlic, Italian seasoning, smoked paprika, salt, and black pepper.
Place the chicken chunks, broccoli florets, cherry tomatoes, and red onion wedges directly onto the prepared baking sheet. Pour the marinade over everything.
Using your hands or a pair of tongs, toss everything together right on the pan until the chicken and vegetables are evenly coated in the oil and spices. Spread them out into a single, even layer so they roast rather than steam.
Bake for 18-22 minutes, tossing halfway through, until the chicken is cooked through (internal temperature reaches 165°F) and the broccoli is tender with charred edges.
Remove from the oven, garnish with extra fresh herbs or a squeeze of fresh lemon juice, and serve immediately.