Preheat oven to 400. Grease and flour 12 muffin cups or line with paper muffin liners. Combine topping ingredients until mixture is crumbly and set aside.
Combine flour, sugar, baking powder, cinnamon, and salt in a large bowl. Whisk butter, milk, and egg together in a separate bowl. Stir milk/egg mixture into the flour mixture and blend just until moistened. Fold in diced peaches. Spoon into muffin cups and sprinkle envenly with topping mixture. Bake for 20-25 minutes, or until a wooden pick inserted in center comes out clean. Remove from pan.