Let's cook.
In a medium bowl, combine the Greek yogurt, fresh lemon juice, dried oregano, garlic powder, salt, and black pepper. Mix well.
Add the cubed chicken to the marinade, ensuring all pieces are coated. Cover the bowl and refrigerate for at least 15 minutes, or up to 4 hours for best flavor.
Preheat your grill to medium-high heat (about 400°F / 200°C) or preheat your oven to 400°F (200°C). If using wooden skewers, soak them in water for 30 minutes prior to assembly to prevent burning.
Thread the marinated chicken, red bell pepper, zucchini, and red onion alternately onto the skewers.
If grilling, place the skewers on the preheated grill. Cook for 15-20 minutes, turning occasionally, until the chicken is cooked through and the vegetables are tender-crisp. If baking, arrange skewers on a baking sheet and bake for 20-25 minutes, flipping halfway through, until chicken reaches an internal temperature of 165°F (74°C).
Remove from heat and let rest for 5 minutes before serving.
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