In a small bowl, mix together ½ cup olive oil, ¼ cup lemon juice, 5 minced garlic cloves, 2 tablespoon Dijon mustard, 2 teaspoon dried oregano, 2 teaspoon dried thyme, 1 teaspoon salt, and ½ teaspoon ground black pepper.
Add ⅔ of the marinade to a large bowl with 5-6 chicken thighs and toss to coat. Let the chicken marinade at room temperature while you prep the rest of the ingredients. NOTE: You can also let this marinade for 1 hr or overnight for even better flavor.
Preheat the oven to 425°F. Arrange all the chopped vegetables: 1 medium red onion, 1 yellow bell pepper, 1 green bell pepper, and 1 zucchini, along with 1 pint cherry tomatoes, onto a large sheet pan in a single layer. Pour the remaining ⅓ of the marinade over the veggies. Use a spatula or tongs to toss everything together and coat evenly.
Make spaces on the sheet pan for the chicken thighs. Place them onto the pan and brush each piece with leftover marinade in the bowl.
Bake in the preheated oven at 425°F for 42-47 minutes, or until the chicken is cooked through and reaches 165°F. (I did 47 minutes, but keep an eye on it!)
Remove the pan from the oven and sprinkle 1 cup Kalamata olives and ½ cup feta cheese over the top of everything. Serve and enjoy!