Cinnamon Muffins

Preheat oven to 400 degrees F. Grease a standard 12 cup muffin pan with cooking spray or use paper liners; set aside.
Sift the dry ingredients together inside a large bowl. Whisk together the wet ingredients until well combined, in a separate medium-sized bowl.
Make a well in the center of the flour mixture for the wet ingredients. Pour the egg mixture into the center of the well. Stir together until just combined.
Combine all the topping and filling ingredients into a small bowl. Add half of the topping and filling mixture, by gently folding it into the muffin batter.
Using a scoop or spoon, add about ¼ cup of the muffin batter into each muffin cup. Sprinkle each with the remaining half of the topping and filling mixture. Bake until muffins are done and a toothpick comes out clean when inserted, about 12 to 15 minutes. Remove from oven and cool about 5 minutes. Transfer carefully to a wire rack and allow them to cool completely.
When the muffins have cooled, whisk together the frosting ingredients and spoon over the muffins and serve.