Preheat the oven to 400° F (200°C)
Lightly grease muffin pan or line with baking cups.
In a bowl, combine the oats and the milk. Let stand for approx. 5 minutes.
In a large bowl, whisk together the flour, baking powder, salt, pumpkin spice, and flax.
Mix egg, brown sugar, vanilla extract, butter, and lemon zest into the oat mixture. Stir to combine.
Poor the oat mixture over the dry ingredients.
Add the peaches and the cranberries.
Fold mixtures until well combined.
Spoon the mixture into muffin pan.
Sprinkle the crumble mixture on top of each portion. (See instructions on crumble below)
Bake for approx. 18 minutes or until tops are golden brown and a toothpick comes out clean.