Preheat the oven to 350°F. Grease a 9" x 13" cake pan.
To make the streusel: Whisk together the sugar, flour, cinnamon, and salt. Cut in the butter until sandy and crumbly. Set aside.
To make the cake: Whisk together the flour, baking soda, baking powder, and salt, and set aside.
In a large bowl, cream together the butter and sugar. Add the vanilla, then the eggs one at a time, scraping down the bowl between each.
Add the flour mixture and the Greek yogurt, alternating between each. Mix just until the batter comes together.
Spread half of the batter into your prepared pan. Take 1/3 of the streusel mixture (or up to 1/2 of it if you want more filling) and sprinkle it evenly over the batter. Pour the remaining batter over the top, spread evenly, and top with the remaining streusel.
Bake for about 55 minutes, or until the top is golden brown and a tester inserted into the center comes out clean or with a few crumbs.