In a large bowl, combine the chicken cubes, BBQ sauce, olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper. Toss to coat the chicken evenly. Cover and marinate in the refrigerator for at least 30 minutes, or up to 2 hours for more flavor.
Preheat your grill or grill pan over medium-high heat.
Thread the marinated chicken, red bell pepper, yellow bell pepper, and red onion onto skewers, alternating between chicken and vegetables.
Grill the skewers for about 10-12 minutes, turning occasionally, until the chicken is cooked through and has nice grill marks. The internal temperature should reach 165°F.
While the skewers are grilling, prepare the salad by placing the mixed greens and cherry tomatoes in a large bowl.
Once the skewers are done, remove them from the grill and let them rest for a few minutes.
Serve the skewers over the salad, sprinkle with feta cheese if desired, and drizzle with ranch dressing or additional BBQ sauce.