Place pears in a greased 8-in. cast-iron skillet or 8-in. square baking dish; sprinkle with sugar. In a small bowl, combine the oats, flour, brown sugar and cinnamon. Cut in butter until mixture resembles coarse crumbs; stir in pecans. Sprinkle over pears. Bake at 350° for 30-35 minutes or until bubbly.
Meanwhile, in a small saucepan, combine the sugar, cornstarch and water. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer.
Remove from the heat. Stir a small amount of hot mixture into egg yolk; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from the heat; stir in the butter, lemon juice and zest. Serve with warm pear crisp.