Prep the chicken: Cut chicken into 1.5-inch cubes. Pat dry with paper towels to help the marinade stick and encourage browning.
Make the marinade: In a large bowl, whisk olive oil, lemon zest, lemon juice, garlic, oregano, smoked paprika, cumin, red pepper flakes (if using), 1.5 teaspoons salt, and 1 teaspoon black pepper.
Marinate: Add chicken to the bowl and toss to coat.
Cover and refrigerate for at least 30 minutes, up to 4 hours. Longer than that can make the chicken mushy due to the lemon.
Prep the veggies: Cut bell peppers and red onion into 1.5-inch chunks. Slice zucchini into 1/2-inch rounds.
Leave cherry tomatoes whole. Toss veggies with a drizzle of olive oil, a pinch of salt, and pepper.
Preheat the grill: Heat to medium-high (about 400–450°F). Clean and oil the grates well to prevent sticking.
Assemble the skewers: Thread chicken and vegetables onto skewers, alternating for color and even cooking.
Don’t pack too tightly; leave a little space for heat circulation.
Grill: Place skewers on the grill. Cook for 10–12 minutes total, turning every 2–3 minutes, until chicken is cooked through and nicely charred in spots. Internal temperature should reach 165°F.
Finish and rest: Transfer to a platter and rest for 3 minutes.
Sprinkle with chopped parsley. Taste and add a pinch of salt or a squeeze of lemon if needed.
Serve: Pair with rice, couscous, naan, pita, or a simple salad. A side of tzatziki, hummus, or chimichurri is excellent.