Prepare the BBQ Chicken: In a large skillet, heat 2 tbsp of olive oil over medium heat. Once hot, add 1 small red onion (thinly sliced) and sauté until soft and translucent, about 5 minutes. Next, add 3 cloves of minced garlic and cook for an additional minute until fragrant. Stir in 2 ½ cups of shredded roasted chicken, ½ tsp paprika, and 1 tsp Worcestershire sauce. Mix well and then pour in 1 cup of BBQ sauce. Stir everything together and let it cook through on low heat for about 5-7 minutes. Set aside.
Make the Garlic Butter: In a small bowl, combine ¼ cup of butter, 2 cloves of minced garlic, and 2 tsp of minced parsley. Microwave for about 20-30 seconds or until melted. Mix well to combine.
Prepare the Bread: Spread the garlic butter mixture generously on one side of each 12 slices of sourdough or sturdy white bread. On the unbuttered side, layer a generous amount of the BBQ chicken mixture, followed by 2 slices of Havarti cheese. Top with another slice of bread, buttered side out.
Cook the Sandwiches: In a skillet over medium heat, place the sandwiches and cook until golden brown, about 4-5 minutes. Carefully flip them over, reduce the heat to low, and continue cooking until the cheese has melted, around 5-7 more minutes. Use a spatula to press down slightly on the sandwiches, ensuring even cooking. You may need to work in batches depending on the size of your skillet.