Prepare the streusel topping. Combine all the ingredients for the streusel topping. It's easiest to mix together with your fingers. Set aside.
Prepare the sliced apples. Mix together with the cinnamon and sugar. Set aside.
Preheat the oven to 425°F. Spray muffin tin with nonstick spray or line pans with muffin liners.
Prepare Muffin batter. With electric mixer, cream together the butter, brown sugar, granulated sugar and eggs. Add the vanilla and Greek yogurt, milk and mix well.
In a separate bowl, whisk together the flour, baking soda, baking powder, cinnamon and salt.
Add the flour mixture to the mixer and combine.
Stir in the chopped apples with a spatula.
Spoon the batter into the muffin cups and fill 2/3 full. Generously sprinkle the streusel topping to completely cover the top of the batter and press down.
Bake at 425°F for five minutes. Without opening the oven, turn it down to 350°F and bake another 16-18 minutes more. Insert toothpick or knife to check if they are done. If it comes out clean, they are ready. Allow to cool for 5 minutes in the pan and then let cool completely on a wire rack.
While the muffins are cooling, prepare the glaze by whisking all the ingredients together. A thicker glaze will set up nicely. Drizzle over the muffins after they have completely cooled.