Preheat and prep. Heat your oven to 425°F (220°C). Line a large sheet pan with parchment for easier cleanup.
Pat the chicken dry with paper towels.
Make the marinade. In a bowl, whisk together the zest and juice of 1.5 lemons, 3 tablespoons olive oil, minced garlic, 1 teaspoon dried oregano, 1 teaspoon paprika, 1 teaspoon kosher salt, 1/2 teaspoon black pepper, and a pinch of red pepper flakes. Add 1 teaspoon honey if you like a subtle balance.
Marinate the chicken. Add the chicken to the bowl and toss to coat. Let it sit while you prep the vegetables, ideally 15–20 minutes.
If marinating longer, refrigerate.
Prep the veggies. Halve baby potatoes (quarter if large). Cut carrots into equal-size sticks. Break broccoli into medium florets.
Wedge the red onion. Aim for similar sizes so they roast evenly.
Season the vegetables. On the sheet pan, toss veggies with 2 tablespoons olive oil, 1 teaspoon kosher salt, 1/2 teaspoon black pepper, and a few sprigs of thyme or rosemary if you have them. Spread into an even layer, leaving space in the center for the chicken.
Add the chicken. Nestle the marinated chicken onto the pan.
Spoon some extra marinade over the top. Save a little lemon for finishing.
Roast. Bake for 20–25 minutes, until the chicken reaches an internal temperature of 165°F (74°C) and the veggies are tender with browned edges. If the vegetables need more color, remove the chicken and broil the veggies for 2–3 minutes.
Finish with freshness. Squeeze the remaining half lemon over everything.
Scatter chopped parsley on top. Taste and adjust salt and pepper.
Rest and serve. Let the chicken rest for 5 minutes, then slice if desired. Serve straight from the pan or plate with any pan juices spooned over the top.