Heat skillet over medium heat. Butter both slices of bread on 1 side. Buttered-side-down, layer 1 slice with Cheddar slices, chicken, red onion, cilantro, BBQ sauce, and Smoked Gouda slices. Place second bread slice on top, buttered-side-up. Preheat skillet; place sandwich in skillet, pressing slightly with backside of spatula. Grill 1-2 minutes or until toasted to your liking. Carefully flip sandwich and continue cooking for an additional 1-2 minutes or until cheese melts. Halve the sandwich to serve.