Preheat oven to 350 degrees F. Lightly coat the bottom and sides of a 9 x 11-inch baking pan with olive oil spray. (Do not use a bigger pan as there won’t be enough batter.)
In a medium bowl, stir together all topping ingredients. Set aside.
In a medium bowl, sift together all dry ingredients.
Using an electric mixer, cream together butter and coconut palm sugar on medium-high speed until creamy, about 1 minute.
On medium speed, beat in eggs. Beat in Greek yogurt (or sour cream) and vanilla extract until smooth, about 1 minute.
On low speed, beat in dry ingredients, mixing just until smooth, about 1 minute.
With a spatula or butter knife, carefully spread 1/2 of the batter into a thin layer in prepared pan. (Batter will be sticky and thick. Make sure batter reaches all margins of pan).
Sprinkle 1/2 of the topping over batter.
Drop spoonfuls of remaining batter over topping. With a butter knife (easier than a spatula) carefully spread, batter, reaching all edges.
Sprinkle remaining topping over batter.
Bake for about 25 minutes or until a toothpick inserted onto the center comes clean. (Do not over-bake or cake will be dry.)
Place on a rack; allow to cool for about 10 minutes before cutting into squares.