Preheat oven to 350°F. Lightly spray a 13x9-inch baking pan with non-stick cooking spray.
For Coffee Cake, stir together flour, sugar, baking powder, baking soda, cinnamon and salt, if desired, in a large bowl. Add pears, sour cream, oil, eggs and vanilla; stir well with a whisk, mashing pears into small pieces. Smooth batter into prepared baking pan.
For Streusel, stir together pecans, oats, brown sugar, cinnamon and butter in a small bowl; sprinkle evenly over batter and pat lightly.
Bake, uncovered, 40 to 45 minutes or until wooden pick inserted in center comes out almost clean. Place on wire rack to cool. Serve warm or at room temperature.