Preheat oven to 350°F Arrange graham squares in single layer in 15x10x1-inch baking pan.
Place butter and sugar in medium saucepan. Bring to boil on medium heat; cook 2 minute Pour over grahams; immediately spread to completely cover all grahams.
Bake 6 to 8 minute or until sugar mixture is lightly browned and bubbly.
Sprinkle with chocolate chunks. Bake an additional 1 to 2 minute or until chocolate is melted. Remove from oven; immediately spread chocolate over grahams. Sprinkle with pecans; press lightly into chocolate with back of spoon.
Cool completely before breaking into squares to serve.