In a small bowl, whisk together the lemon juice, olive oil, garlic, oregano, Dijon mustard, salt, and black pepper to make the marinade.
Spread the zucchini, yellow bell pepper, red onion, and tomatoes on a sheet pan. Drizzle with half the marinade and toss to coat. Roast for 15 minutes.
While the vegetables roast, place the chicken breast slices in a bowl. Pour the remaining marinade over the chicken and let sit for 10 minutes.
After 15 minutes, remove the sheet pan from the oven. Nestle the marinated chicken among the vegetables.
Return the pan to the oven and bake for 10 minutes.
Remove the pan, scatter kalamata olives and crumbled feta over the top, and bake for another 5–8 minutes, or until the chicken is cooked through (165°F / 74°C).
Sprinkle with chopped parsley and serve warm.
Notes
Read First: Before cooking, read the full recipe and Ingredient Notes. The step-by-step photos and tips throughout the post will help guide you.
Cut Evenly: Chop vegetables into similar sizes to ensure even roasting.
Oven Rack Placement: Position the rack in the center of the oven for balanced cooking.
Check Chicken Temperature: Use an instant-read thermometer to confirm the chicken reaches 165°F (74°C).