In a large mixing bowl, combine the Greek yogurt, 4 tablespoons of olive oil, minced garlic, lemon zest and juice, 1 teaspoon of kosher salt, ¼ teaspoon of black pepper, 1 teaspoon of Greek seasoning, ½ teaspoon of ground fennel, and honey. Whisk until smooth and well combined.
Add the chicken breasts to the marinade, ensuring each piece is fully coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for maximum flavor.
Preheat your oven to 400°F (200°C). This temperature is crucial for achieving that perfect roasted finish.
While the chicken marinates, slice the cauliflower into bite-sized florets. In a separate bowl, toss the cauliflower with the remaining 2 tablespoons of olive oil, ½ teaspoon of kosher salt, ¼ teaspoon of black pepper, 1 teaspoon of Greek seasoning, and ½ teaspoon of ground fennel until evenly coated.
Spread the marinated chicken breasts in the center of the sheet pan. Arrange the seasoned cauliflower florets around the chicken. If desired, scatter halved cherry or Glory tomatoes over the pan for an extra burst of flavor.
Place the sheet pan in the preheated oven and roast for 25-30 minutes, or until the chicken is cooked through (internal temperature should reach 165°F or 75°C) and the cauliflower is tender and golden.
Once out of the oven, sprinkle the dish with chopped fresh parsley for a pop of color and freshness. Serve hot, either on its own or with a side of your favorite grain or bread.