Preheat oven to 400°F. Line the cups of a standard muffin tin with paper baking liners, or mist with nonstick cooking spray.

To prepare the topping, combine pecans, brown sugar, flour, and cinnamon together in a small bowl. Add melted butter, stirring until mixture is crumbly. Set aside.

To prepare muffins, whisk flour, sugar, baking powder, cinnamon, and salt together in a large bowl. In a small bowl, whisk melted butter, milk, and egg until blended. Pour into flour mixture and stir until moistened. Fold in peaches.

Spoon batter into muffin cups. Sprinkle topping over batter. Bake 20–25 minutes, or until a wooden pick inserted in center comes out clean.