Add the oil to a large pan over medium heat, then add the onions and cook for 2-3 minutes, stirring until slightly softened. Add the chicken, garlic powder, paprika, Worcestershire sauce, and BBQ sauce, mixing until everything is well-coated. Turn off the heat and set the pan aside.

In a small microwaveable bowl, combine the butter, garlic powder, and dried parsley, then microwave for 10-30 seconds or until just melted. Place the 8 pieces of bread on parchment paper and use a basting brush to spread the butter mixture on one side of each piece.

Flip each piece of bread over so the buttered side is down. Add a slice of cheese to 4 of the slices, then evenly divide the chicken mixture on top of each cheese slice. Place another slice of cheese on top of the chicken mixture, then top with the remaining bread slices, ensuring the buttered sides are facing out.

Spray a large pan with non-stick cooking spray and cook the sandwiches over medium to low heat for 3-4 minutes on each side, or until the bread reaches your desired level of golden brown. Slice, serve, and enjoy!