1) Preheat oven to 350 degrees F.
2) Wash cranberries well, then drain and immediately toss with 1/4 cup sugar. Set aside.
3) Whisk together flour, baking powder, baking soda, and salt in a small bowl and work streusel ingredients together with your hands or a fork in a separate bowl.
4) In a large bowl with a hand mixer, cream together butter, sugar, and orange zest until smooth. Then mix in vanilla extract and eggs one at a time.
5) Mix in Greek yogurt, then the flour ingredients. Finally add buttermilk and slowly mix until batter is smooth. Then fold in sugar-coated cranberries.
6) Pour half the batter into a lightly buttered 8×8 baking dish. Top with half of the streusel mixture.
7) Top with last half of the batter and the last of the streusel.
8) Bake the coffee cake at 350 degrees F. for about an hour until the center is just set. Remove coffee cake and let it cool for 20 minutes or so.
9) Slice coffee cake into 9 even pieces and serve while warm or at room temperature.