Heat the oven to 350 degrees F. Grease a 9-inch springform pan.
In a large bowl combine the flour, oats, sugar, baking powder, baking soda, cinnamon, and salt. Set aside.
Combine the eggs, 1/4 cup soft butter, and sour cream. Add the dry ingredients and mix with a spoon just until the mixture is well combined.
Spread the mixture into the prepared springform pan. Top the batter with the chopped apples.
For the streusel combine the brown sugar, flour, oats, and cinnamon. Add the butter and mix until well combined. Toss in the pecans.
Sprinkle the streusel over top of the apples. With your fingertips lightly press the streusel into the batter.
Place the coffee cake into the preheated oven and bake for 40 to 45 minutes or until a wooden pick comes out clean.