Set oven control to broil. Butter each bun half, and place on cookie sheet, butter sides up. Broil with tops 6 inches from heat for a minute or two or until golden brown. Remove from oven, leaving broiler on, and set top buns aside. Pile some of the chicken onto each bottom bun; top with cheese, green onions and/or jalapeños, and place back under broiler until cheese is melted and bubbling. Top with top buns, and serve warm.