Heat oven to 350°F.
Line 15x10x1-inch pan with heavy-duty foil. Spray foil with cooking spray. Spread cereal evenly in pan.
In 2-quart saucepan, heat butter and brown sugar. Using whisk, mix butter and brown sugar together as butter melts. Heat to boiling over medium-high heat, stirring occasionally. Reduce heat to medium. Boil 2 minutes without stirring. Immediately pour mixture evenly over cereal in pan.
Bake 12 minutes. Sprinkle chocolate chips on top. Let stand 5 minutes. Spread melted chocolate; top with pecans. Cool completely, about 1 hour. Refrigerate 20 minutes to set chocolate; break into pieces. Store covered in refrigerator up to one week.