BBQ Chicken Melt

Heat grill pan over medium-high heat. Brush with olive oil. Season chicken on both sides with salt and pepper. Place on pan and grill until cooked through, about 4-5 minutes per side. During the last minute of cooking, brush chicken breasts with barbecue sauce. Remove chicken and let rest of 5 minutes. Slice crosswise. Rub olive oil on onions and season with salt and pepper. Grease the pan a bit more with olive oil. Add onions and cook until softened, about 2-3 minutes per side, brushing the onions with the sauce during the last minute of cooking. Turn off the heat and carefully wipe pan to remove any blackened bits. Assemble the sandwiches. Lightly brush outside of bread with olive oil. Add chicken to one slice. Top with more sauce, then add the onions, cheese and other slice of bread. Repeat process to make 3 more sandwiches. Reheat grill pan. Add sandwiches to hot pan and place a heavy skillet ( such as cast iron) on top of the sandwiches to press down. Cook until cheese is melted.