Combine flour, baking soda, baking powder & salt in another bowl. Slowly add to wet mixture. Mix until just incorporated.
In a separate bowl, prepare streusel by stirring all the dry ingredients. Add melted butter & mix well with a fork until combined & crumbly.
Spread half of the cake batter into the bottom of a greased 13x9" pan. Sprinkle half of the streusel on top. Dollop the remaining cake batter on top of the streusel & spread it the best you can (the batter is thick.) Sprinkle remaining streusel over the cake.