Preheat oven to 400 degrees, and grease or line a 12 cup muffin pan.
In a medium bowl, combine the oat topping ingredients together and stir to combine, set aside.
In a large bowl whisk together the sugar, cooled melted butter, egg, milk, and vanilla extract together.
In a separate bowl, whisk together the flour, baking powder, and salt together.
Gently stir the dry ingredients into the wet just until combined. Gently fold in the peeled, chopped peaches. Scoop evenly into the muffin tins. Spoon oat crumb topping onto each muffin and press down lightly. Bake for 19-21 minutes or until a toothpick comes out clean.
I love to serve mine warm with butter and honey. They would also be a really yummy dessert served with a scoop of vanilla ice cream!