In a large bowl, whisk together buffalo sauce, ranch seasoning, olive oil, lemon juice (if using), salt, and pepper. Add chicken cubes and toss to coat evenly. Cover and refrigerate for at least 30 minutes or up to 4 hours for deeper flavor.
If using wooden skewers, soak them in water for 30 minutes to prevent burning on the grill.
Thread marinated chicken pieces onto skewers, leaving a little space between each piece for even cooking.
Preheat grill to medium-high heat (about 400°F / 200°C). Place skewers on the grill and cook for 5–7 minutes per side, or until chicken is cooked through and slightly charred.
Remove from grill and rest for a few minutes. Serve with ranch or blue cheese dressing and sprinkle with chopped parsley or crumbled blue cheese if desired.