In a large bowl, combine the flour, brown sugar, baking powder and salt. In another bowl, combine the milk, oil, egg and vanilla. Stir into dry ingredients just until moistened. Fold in peaches and pecans.
Fill greased or paper-lined muffin cups two-thirds full. Combine topping ingredients until crumbly; sprinkle over batter.
Bake at 400° for 15-18 minutes or until a toothpick inserted near the center comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Yield: 1 dozen.