Cut chicken breasts into 1-inch cubes and set aside. Cut all bell peppers (red, orange, and green) into 1-inch squares. Cut the large red onion into 1-inch chunks, separating the layers so they don't stay clumped together. Have the pineapple chunks ready (drain if using canned, reserving the juice). Mince the garlic cloves fresh—this makes a real difference in the marinade's brightness compared to pre-minced.

In a bowl, whisk together ketchup, soy sauce, brown sugar, pineapple juice, sesame oil, ground ginger, minced garlic, sriracha sauce, rice vinegar, and smoked paprika until the brown sugar fully dissolves and everything is well combined. Measure out and set aside 1/2 cup of the marinade in a separate bowl for the vegetables and basting. This split approach ensures you have enough flavor on both the chicken and vegetables, and keeps some marinade for brushing during grilling.

Place the chicken cubes into the remaining marinade (the portion you didn't set aside). Toss well to coat all pieces evenly. Cover and refrigerate for at least 30 minutes, but ideally 2-4 hours for deeper flavor development. This resting time allows the soy sauce and ginger to penetrate the chicken while the acids begin to tenderize it.

Remove the marinated chicken from the refrigerator about 10 minutes before grilling to bring it closer to room temperature. In a separate bowl, toss the prepared bell peppers, pineapple chunks, and red onion pieces with the reserved 1/2 cup marinade from Step 2 until everything is well coated. Thread the chicken, vegetables, and pineapple onto skewers, alternating items to ensure even cooking and a good mix in each bite. I like to start and end each skewer with a piece of red onion because it holds the other pieces in place nicely.

Preheat your grill to 400°F. Once hot, place the loaded skewers directly on the grill grates. Grill for 12-16 minutes total, turning every 2-3 minutes to ensure even cooking and prevent sticking. Brush generously with any remaining marinade from Step 2 each time you turn the skewers. The chicken is done when it reaches an internal temperature of 165°F and the exterior has light charring; the vegetables should be tender with caramelized edges.

Transfer the grilled kabobs to a serving platter and let them rest for 5 minutes before serving. This brief resting period allows the juices to redistribute throughout the chicken, keeping it tender and moist. Serve immediately with rice, jasmine tea, or your favorite sides.