Preheat the oven to 375 degrees F. Grease a 13- by 9-inch pan.
For the filling: In a medium bowl, stir together the pecans, brown sugar and cinnamon until nicely combined and the pecans are fully coated.
For the glaze: In a second medium bowl, whisk together the confectioners' sugar, lemon juice and milk until all the sugar is fully incorporated and there are no lumps. Set the glaze to the side.
For the cake: Into a large bowl, add the cake mix, sour cream, vegetable oil, sugar, 1/4 cup water, flour and eggs. Using an electric mixer, beat the ingredients until fully combined, about 4 minutes. Pour about half of the batter into the prepared pan. Spread the pecan filling on top and swirl into the batter. Pour the next half of the batter over and spread to make an even layer.
Bake until a toothpick inserted in the center comes out clean, about 30 minutes. Remove from the oven, place on a cooling rack and let cool in the pan for 30 minutes. Then invert the cake onto a plate or platter, and let cool completely.
Whisk the glaze a bit to make sure it's still smooth and then drizzle all over the cake. Let the glaze set a bit and serve!