Prepare Streusel: Stir together pecans and next 4 ingredients until crumbly.
Prepare Muffins: Preheat oven to 400º. Combine flour and next 4 ingredients in a large bowl; make a well in center of mixture. Stir together butter, milk, and egg; add to dry ingredients, stirring just until moistened. Gently stir in peaches.
Place paper baking cups in 1 (12-cup) muffin pan, and coat with cooking spray; spoon batter into cups, filling two-thirds full. Sprinkle with Pecan Streusel.
Bake at 400º for 20 to 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes; remove from pan, and serve warm or at room temperature.