Heat vegetable oil in a deep, heavy-bottomed saucepan to 350°F (175°C).
Whisk together flour, sugar, baking powder, salt, and cinnamon in a large mixing bowl.
In a separate container, whisk the egg, 1/3 cup milk, and 1 teaspoon vanilla extract.
Combine the wet and dry ingredients, stirring until a thick batter forms.
Fold the diced apples into the batter until evenly distributed.
Drop tablespoon-sized portions of batter into the hot oil, frying in batches of 4-5 to maintain oil temperature.
Fry for 2 minutes per side or until the exterior is deep golden brown and the interior is fully cooked.
Transfer the fried bites to a wire rack or paper-towel-lined plate to drain.
Whisk the powdered sugar, 2 tablespoons milk, and 0.5 teaspoon vanilla extract in a small bowl to create a glaze.
Drizzle the glaze over the warm fritter bites and serve immediately.