In a medium bowl, whisk together onion powder, black pepper, salt, garlic powder, and chili powder. Add chicken, tossing to coat the cubes well. Refrigerate and marinate the chicken for 30 minutes to 2 hours.
Preheat grill or grill pan when ready to cook. Soak wooden skewers in a shallow pan filled with cold water for 15 minutes.
Pat dry the wooden skewers.
Build the skewers by alternating pieces of chicken, onion, bell peppers and zucchini.
Each skewer should have at least 3 to 4 pieces of chicken.
Oil the grill or grill pan lightly with vegetable oil.
Cook the skewers for 12 to 15 minutes, rotating throughout the cooking process, until the chicken is cooked through. Remove from grill and sprinkle with chopped fresh cilantro. Serve immediately.