Preheat oven to 350°F (175°C).

Grease a 13x9-inch baking dish.

In a large bowl, cream together the softened butter and sugar until light and fluffy.

Beat in the eggs, one at a time, beating well after each addition.

Stir in the vanilla extract.

In a separate bowl, combine the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the creamed mixture, alternating with the sour cream, and beat until just combined.

Pour half of the batter into the prepared baking dish.

In a bowl, combine the peach pie filling and drained sliced peaches.

Spread the peach mixture evenly over the batter.

Drop the remaining batter by tablespoonfuls over the peach filling.

In a separate bowl, combine the brown sugar, flour, oats, and cinnamon.

Cut in the cold, cubed butter until the mixture resembles coarse crumbs.

Sprinkle the topping evenly over the batter.

Bake for 70-75 minutes, or until a toothpick inserted into the center comes out clean.

Let the coffee cake cool completely on a wire rack.

In a small bowl, whisk together the confectioners' sugar and milk until smooth, adding more milk as needed to reach desired consistency.

Drizzle the glaze over the cooled coffee cake.

Slice and serve.