Preheat oven to 375 degrees Fahrenheit, and lightly grease a 13x18-inch baking sheet.
Lay 4 boneless skinless chicken breast out onto the pan evenly spaced apart.
Cut 1 medium red onion into bite-size chunks and slice 2 medium zucchini, about 1/4-inch thick. Spread out the onion, zucchini slices, 1 pint cherry or grape tomatoes, and 1 cup pitted kalamata olives onto the pan, surrounding the chicken. Sprinkle 1/4 cup sliced pepperoncinis on top of the chicken.
In a small bowl, whisk together 1/4 cup olive oil, 2 tablespoons white wine vinegar, 2 tablespoons lemon juice, 5 teaspoons minced garlic, 2 teaspoons dried oregano, 1 teaspoon dried basil, 1 teaspoon ground cumin, 1 teaspoon salt, and 1 teaspoon paprika
Drizzle the dressing over both the chicken and veggies. Give the veggies a quick toss to coat.
Bake in the preheated oven for around 35 minutes, or until chicken reaches an internal temperature of 165℉.
Remove the pan from the oven and sprinkle with 1/2 cup crumbled feta cheese. Serve hot.