In a bowl, combine 2 cups of plain Greek yogurt, 1/4 cup chopped fresh dill, 1 tablespoon grated lemon zest, 2 tablespoons lemon juice, and 1 grated garlic clove. Season with kosher salt and black pepper to taste. Whisk until creamy and smooth, then cover and refrigerate for at least 30 minutes.

In a separate bowl, blend 1 tablespoon garlic powder, 1 tablespoon lemon-pepper seasoning, 2 teaspoons crushed fennel seeds, 2 teaspoons dried oregano, and a pinch of salt. Add 1/4 cup of vegetable oil, stirring to combine. Cut 2 1/4 pounds of chicken thighs into even pieces, add to the marinade, and let marinate for a minimum of 30 minutes.

Preheat your grill to medium-high heat, aiming for around 400°F. If using wooden skewers, soak them in water for 30 minutes to prevent burning.

Remove chicken from marinade and thread onto soaked or metal skewers, alternating with sweet onion wedges and thickly sliced zucchini.

Place the skewers on the preheated grill and cook for approximately 10 to 15 minutes. Turn occasionally, ensuring chicken is fully cooked to an internal temperature of 165°F.

Once grilled to perfection, remove the kebabs from the grill and let rest for a few minutes before serving warm with the chilled dill yogurt sauce and pita bread.