In an 8-9 inch shallow baking dish, spread pear slices. Spoon lemon juice over pears slices. Spoon lemon juice over pears and toss to coat. In a small bowl, blend flour and light brown sugar, cinnamon and butter with a pastry blender or fork. Add chopped pecans and mix well. Sprinkle mixture over pears and microwave, uncovered on high for 8-10 minutes or until bubbly. let stand 5 minutes. Serve warm.