Preheat your waffle iron according to the manufacturer's instructions.
In a large mixing bowl, whisk together the flour, baking powder, cinnamon, salt, and granulated sugar until well combined.
In another bowl, beat the eggs and then add the milk, melted butter, and vanilla extract. Mix until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Gently fold in the diced apples until evenly distributed in the batter.
Lightly grease the waffle iron with cooking spray. Pour enough batter into the waffle iron to cover the surface (about 1/2 to 3/4 cup, depending on the size of your waffle iron). Close the lid and cook until golden brown and crispy, about 3-5 minutes.
While the waffles are cooking, prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract in a small bowl until smooth.
Once the waffles are done, remove them from the waffle iron and drizzle with the glaze while they are still warm.
Serve immediately and enjoy your delicious apple fritter waffle donuts!