In a large bowl, whisk together flour, brown sugar, cinnamon, nutmeg and salt.
Add butter.
Mix in the pecans and oats until just combined.
Transfer the streusel on top of the apples and gently spread into an even layer without pressing it down.
Bake for 40-45 minutes or until the apples are soft and the crumble is golden brown.
Cool for at least 15 minutes before serving.