Dice the chicken breast into 3 cm cubes. Pat them dry with a kitchen towel.
Next, chop the peppers, zucchini, and onion into pieces similar in size to the chicken cubes.
Prepare the Marinade: In a bowl, mix together the black pepper, salt, paprika, garlic powder, yogurt, and ground cumin until well combined.
Marinate the Chicken: Place the chicken cubes in a shallow dish or a resealable plastic bag. Pour the marinade over the chicken, ensuring each piece is well coated. Cover the dish or seal the bag, then refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to meld.
Prepare the Skewers: If you're using wooden skewers, soak them in water for about 30 minutes to prevent them from burning during grilling. Once soaked, thread the marinated chicken pieces onto the skewers, alternating with chunks of red onion, bell pepper, and slices of zucchini.
Preheat the Grill: Preheat your grill to medium-high heat, around 375-400°F (190-200°C). Place the assembled kebabs on the preheated grill and cook for about 5 minutes on each side, or until the chicken is cooked through and the vegetables are tender, with a slight char on the edges.
Serve: Remove the kebabs from the grill and let them rest for a few minutes. Serve the chicken kebabs hot, accompanied by sliced tomatoes, cucumbers, and warm pita bread.