Preheat your oven to 375. To prep your muffin pan, use a pastry brush or similar item to generously coat each of the muffin cups with the oil. Then place the muffin pan into your oven to preheat.
In a large bowl, use a whisk to combine together the flour, baking powder, baking soda, sugar, and pumpkin spice. Then make a well in the center of the ingredients.
Next, in a medium bowl, use a clean whisk or a fork to combine together the eggs, milk, vanilla extract and melted butter. Then pour this mixture into the well that you created in the dry ingredients and mix until just combined.
Carefully remove the warm pan from your oven and place in on a heatproof area of your work surface.
Next, use a rubber spatula or similar item to fold in the apple pieces and the vinegar into the batter. Use a small cookie scoop to scoop the batter into the warm muffin cups, about three quarters of the way full.
Carefully return the muffin pan to your oven and bake your muffins for 18-20 minutes or until a toothpick inserted into the center comes out clean and the edges begin to brown. You can check on the muffins after 15 minutes of baking.
When your muffins are done baking, let them sit in the muffin pan for five minutes before transferring them to a cooling rack to fully cool.
To make the glaze, simply combine together the glaze ingredients, making ingredient adjustments as needed until you reach your desired consistency. Then use a spoon to drizzle it over the cooled muffins while they are still warm.